Trouble shooting complex CH problems

[CMJ]

Hi all

My first post on here! Have read loads of useful info but couldn't find the answers to my problems so thought I'd put it to you all. Hope someone out there can help.

We have a fairly complicated sealed system installed in our house and I'm tearing my hair out trying to resolve issues that have been ongoing since it was installed 2 years ago. I now realise the original installer wasn't up to the job, but he's since moved abroad and left me to pick up the pieces.

In a nutshell, we have got through 2 heat exchangers in our boiler in as many years. Same problem both times; the heat exchanger leaks system water across into the condensate resulting in rapid loss of pressure and frequent topping up. Both myself and the boiler engineers are completely at a loss to understand how this could happen twice in a brand new boiler, and so I've been looking at the system design to see whether we have a design fault somewhere that could be contributing to it.

The system comprises a Worcester Greenstar 40CDI conventional coupled to a 280 Litre Thermostore cylinder which provides the DHW and also the underfloor heating in 2 zones of the house. The rest of the house (a further 3 zones) is heated by standard rads, a whopping 22 of them in total which are run directly off the flow/return of the boiler with zone valves on the flow. It was a completely new system/rads/pipework 2 years ago. The Thermostore was originally installed because we were going to fit solar hot water panels, but this never materialised so in effect the Thermostore wasn't really necessary/the best option, but we'd already bought it and it had been fitted.

The Thermostore requires the boiler to operate at maximum output (88 degrees) in order to provide good DHW recovery. Not ideal given that I thought condensing boilers worked most efficiently around the 60 degree mark? Anyway, if the boiler is turned down the DHW is depleted fairly quickly and recovery is slow but at maximum output the DHW is really good. Naturally, running the system at max output means that all the rads get unnecessarily hot (dangerously hot) and causes a fair amount of expansion in the system. It also means that when the boiler is running hot and then all the zone valves close (because the zones have reached temp) there is a lot of heat remaining in the boiler. To deal with this the main pump has an overrun for a few minutes, and there is an automatic bypass valve which feeds a dedicated bypass radiator circuit. However, this bypass circuit does not always seem to operate and occasionally the boiler has overheated and let off steam from its auto bottle vent.

There is an expansion vessel on the pipework, although I notice this is only an 18L vessel and I also notice it's connected to the flow pipe AFTER the auto bypass valve. I have read elsewhere on this forum that it should be potentially much bigger (perhaps 50L?) and also fitted on the return pipework? I have checked the expansion vessel works ie. no water from the valve.

I have a number of questions:

1. Any ideas why any of the above would cause the heat exchanger problem mentioned? Would running the system at max output be a bearing factor or should it be capable of this?

2. Is the 18L expansion vessel and it's position in the system adequate? If not what should I fit, and where in the system?

3. Why would the auto-bypass valve sometimes not operate?

4. Can anyone suggest a way in which I can alter this system fairly simply so that I can run the boiler at max output but have the rads run at a more reasonable temp?

5. We are going to have to drain, clean and refill the system in order to change the heat exchanger again. Do you have any guidance on how much inhibitor to use in a system of this size? I was going to use Sentinel X100 - is this a good choice? We have noticed that the existing system water is a murky brown colour, not good at all. We can only assume this is because of the frequent re-filling that has diluted the existing inhibitor which has effectively been lost down the condensate pipe.

6. We recently fitted a water softener. Can I (should I?) refill the system with softened water? I have seen confilcting advice on this point and wonder if anyone has first hand experience of it.

I apologise for the enormous post, but hope someone out there can shed some light on these problems.

Cheers

 

[Agile]

I dont have time to read everything but be aware that Worcester ( sorry Jo ) boilers do have alloy HEs and not stainless like the better boilers.

Since that should be covered by the warranty they should be only a minor inconvenience to you.

Your problem seems to be that you dont want to pay for a good professional to sort it out for you.

"Murky water inplies dirty water that was never power flushed or chemically cleaned or inhibited.

You have not disclosed your location and perhaps this is intentional because you have to intentionally skip a field when registering! So I am left thinking you DONT want to find a professional but expect to get free info from here to solve it yourself. Thats encouraged because you employed a cheap nupty in the beginning.

You say the installer has "gone abroad" ! In our terms that usually means it was an unregistered East European plumber who could probably not even read the installation manuals and was not gas registered.

Any true professional would have told you that a thermal store has limited capacity at the temperatures supplied by condensing boilers. If there was any good reason to use them then they have to be sized accordingly.

Feel free to explain the real background.

Please understand that I often have to go to sort out the problems caused by nupty plumbers usually employed by cost cutting ( profit building ) builders.

Tony

 

[Homesafe]

Hi all

My first post on here! Have read loads of useful info but couldn't find the answers to my problems so thought I'd put it to you all. Hope someone out there can help.

We have a fairly complicated sealed system installed in our house and I'm tearing my hair out trying to resolve issues that have been ongoing since it was installed 2 years ago. I now realise the original installer wasn't up to the job, but he's since moved abroad and left me to pick up the pieces.

In a nutshell, we have got through 2 heat exchangers in our boiler in as many years. Same problem both times; the heat exchanger leaks system water across into the condensate resulting in rapid loss of pressure and frequent topping up. Both myself and the boiler engineers are completely at a loss to understand how this could happen twice in a brand new boiler, and so I've been looking at the system design to see whether we have a design fault somewhere that could be contributing to it.

The system comprises a Worcester Greenstar 40CDI conventional coupled to a 280 Litre Thermostore cylinder which provides the DHW and also the underfloor heating in 2 zones of the house. The rest of the house (a further 3 zones) is heated by standard rads, a whopping 22 of them in total which are run directly off the flow/return of the boiler with zone valves on the flow. It was a completely new system/rads/pipework 2 years ago. The Thermostore was originally installed because we were going to fit solar hot water panels, but this never materialised so in effect the Thermostore wasn't really necessary/the best option, but we'd already bought it and it had been fitted.

The Thermostore requires the boiler to operate at maximum output (88 degrees) in order to provide good DHW recovery. Not ideal given that I thought condensing boilers worked most efficiently around the 60 degree mark? Anyway, if the boiler is turned down the DHW is depleted fairly quickly and recovery is slow but at maximum output the DHW is really good. Naturally, running the system at max output means that all the rads get unnecessarily hot (dangerously hot) and causes a fair amount of expansion in the system. It also means that when the boiler is running hot and then all the zone valves close (because the zones have reached temp) there is a lot of heat remaining in the boiler. To deal with this the main pump has an overrun for a few minutes, and there is an automatic bypass valve which feeds a dedicated bypass radiator circuit. However, this bypass circuit does not always seem to operate and occasionally the boiler has overheated and let off steam from its auto bottle vent.

There is an expansion vessel on the pipework, although I notice this is only an 18L vessel and I also notice it's connected to the flow pipe AFTER the auto bypass valve. I have read elsewhere on this forum that it should be potentially much bigger (perhaps 50L?) and also fitted on the return pipework? I have checked the expansion vessel works ie. no water from the valve.

I have a number of questions:

1. Any ideas why any of the above would cause the heat exchanger problem mentioned? Would running the system at max output be a bearing factor or should it be capable of this?

2. Is the 18L expansion vessel and it's position in the system adequate? If not what should I fit, and where in the system?

3. Why would the auto-bypass valve sometimes not operate?

4. Can anyone suggest a way in which I can alter this system fairly simply so that I can run the boiler at max output but have the rads run at a more reasonable temp?
5. We are going to have to drain, clean and refill the system in order to change the heat exchanger again. Do you have any guidance on how much inhibitor to use in a system of this size? I was going to use Sentinel X100 - is this a good choice? We have noticed that the existing system water is a murky brown colour, not good at all. We can only assume this is because of the frequent re-filling that has diluted the existing inhibitor which has effectively been lost down the condensate pipe.

6. We recently fitted a water softener. Can I (should I?) refill the system with softened water? I have seen confilcting advice on this point and wonder if anyone has first hand experience of it.

I apologise for the enormous post, but hope someone out there can shed some light on these problems.

Cheers

all the above suggest that you are not being straight.

the water being murky brown , means it probably has never been flushed/treated properly, this is probably the first time you have thought about cleaning and inhibitor's.

you might get someone to give you advice, but your main problem is an illegal install.

 

[Agile]

He may be new to gas but he seems to have reached the correct conclusion very quickly here!

 

[tamz]

Agile you probably hit the nail right on the head with this

Your problem seems to be that you dont want to pay for a good professional to sort it out for you.

 

[gordonspants]

I think that's right - it's not been fitted correctly.
I read this last night - I'm responding not because I know much about heating, but because I have a thermal store, kind of designed between me (about 20% - a crazy wishlist partly taken off the internet) and a bloody good plumber (the other 80% - a shedload of experience).

Toughest part of the whole thing was finding an installer who *really* understood everything. Doesn't sound like you've ben so lucky.

Q's I *think* I know the answers to are...

1 and 2 - 22 rads, a spare 280l of water and only an 18l expansion vessel might be a good place to start to solve the boiler virtually exploding. But you knew that anyway, right? Does the floor in the ufh-heated areas go all bumpy when your boiler is about to go pop? I bet the pipework is under some serious stress. My store is a similar size to yours, and I have 25l of expansion just for the store, never mind the rest of the system.

4 - a blending valve would control rad temps (TMV) - smilar to what I'm really really hoping is fitted on your ufh system. You could even get clever and fit weather compensation.

5 - Inhibitor quantity needs to be worked out for the entire heating system - yours sounds huge - and THEN add another 280 litres of 'system' on for the thermal store. Mine has 3 bottles of X100 in, and every time I clean the magnaclean out I mop the water out of it and pour in more X100. Whole system (part 1970's) was chemically cleaned 6 months before fitting store. If you're in a hard water area you need it spotless apparently.

You do have a magnaclean, had the system cleaned out/flushed, and checked the plumbers previous work with thermal stores and solar? Did the supplier of the store get involved with system sizing, expansion vessel sizing etc? If you have to run the store being fed 88 degree heat, something's not right with the hot water side of things. My store works in the dead of winter at a max of 70-75, summer I turn it down to 60-65 or less.

You need a professional who understands thermal stores, solar and underfloor heating. Not your standard combi-boiler plumber - I found that out just asking people for quotes and getting blank looks. My guy fits Nuheat stores, solar, ufh, etc etc. Without that serious indepth knowledge, I'd have been stuffed, probably in the situation you're in now. Cheque book time - sorry.

 

[CMJ]

Crikey! Seems I've inadvertantly fired up some emotions here. Perhaps I did not provide sufficient info in my original post. Please forgive me, it was my 1st post after all.

Taking the various remarks in turn:

Agile: Thanks for your response.

What is the signifcance of the alloy HE as opposed to stainless on "better boilers"? Does this mean it's more likely to leak/fail or are you making me aware of that for some other reason?

I'm clearly not an expert and I'm not trying to become one either, although I am a 'techincal type' who likes to understand how things work (or indeed why they don't), hence me posting on here. I'm a householder who is very, very eager to get this wretched system working properly after 2 years of hell! I'm happy to pay a Pro to solve my problems but I haven't been able to find one yet who a] understands the intricacies of a system combining this particular thermal store (it's from a company called Chelmer) with complex controls, UFH and rad zones or b] take on a system that someone has (in my opinion) bodged previously. Or both a] and b]. It's hardly a surprise though.

I am in Bristol - no secret! I was not aware of a field to enter a location when I registered. If you or anyone can recommend a great heating engineer in my area with experience of Thermal Store (ideally Chelmer), UFH, rad zones, networked Heatmiser controls etc, that would be most helpful.

The "murky water" I'm unable to fully explain because I was not the installer. I *believe* it was flushed and inhibitor was added, however there were a couple of major leaks and I suspect that additional inhibitor may not have been added after resolving these problems. That would mean the inhibitor was very diluted. He may not have even used adequate inhibitor in the first place. Also, the HE was replaced by Worcester a year ago and they may not have added more inhibitor (they had to partially drain down because there are no isolation valves on this boiler). I don't know. Whatever the initial concentration of inhibitor, I'm certain that it is very, very diluted now because I am having to top up the system twice a day from almost 0 bar to 1 bar. That's a lot of fresh water.

Incidentally, this was no cheap numpty. I entrusted someone who had fitted the system (albeit very much simpler) in my previous house, which I was pleased with, so thought he would do a good job again. With hindsight he was not up to the job: both he and I should have realised that early on. He was not an 'Eastern European' either (although that remark sounds unkind, and I apologise to any EEs as I do not mean offence), he was a British chap and was CORGI registered as it was back then (2 years ago). Oh, and he was a plumbing/gas tutor at the main local college too. Given the cock-ups I believe he made here (some of which I'm only just discovering from my own research) it's a miracle that any of his students pass. I am so digusted with the mess I've been left to sort out, I can tell you.

I'm sure you're right about the Thermal Stores. To be honest, I was 'sold' on the idea because of a Home Improvement Show I attended. I came away from the Chelmer stand thinking that this would be the perfect thing to fit in our new house, which was at the system design stage. I think I was mainly blinded by the fact that this particular system had a solar coil input which in effect would heat both the DHW and the UFH part of the cylinder (sorry, thermal store) which would mean the UFH part might be run entirely from solar because of the lower heat demand of UFH. Unfortunately I did not fit the solar panels because of Conservation Area bureaucracy which delayed the project too much and I gave up on the idea. I wish I had installed a regular unvented cylinder now. Like the other post from gordonspants, it was a system partly specified (or rather suggested) by me and mostly designed by the installer. Big mistakes made, I've learned my lesson well and truly.

Hope you might be able to help further now I have given you some background.

Newgas: Thank you also for your response.

Please see the comments in my response to Agile, above.

This was no illegal installation. I paid a pricely sum to a CORGI regsitered installer who was qualified to install unvented systems under Building Regs.

Gordonspanst: Thanks for your helpful information. I will post a separate reply to you as this one is already too long!

Cheers.

 

[D_Hailsham]

Have you considered contacting Chelmer and asking for their advice?

Chelmer Heating Services
Unit 12A Baddow Park
West Hanningfield Road
Great Baddow
Chelmsford
Essex
CM2 7SY

T: 01245 471111
F: 01245 471117
E: sales @ chelmerheating.co.uk

 

[Agile]

Wow, that sounds so close to where the once mighty Marconi company used to live!

Any cylinder even if designed for solar input will work equally without it.

Tony

 

[CMJ]

>>Have you considered contacting Chelmer and asking for their advice?

Yes, I have spoken to them on numerous occasions over the last 2 years, sometimes helpful, sometimes not. This installation was not designed by them so they are of limited help.

I have contacted their local recommended installer who was not much help. I get the impression most good people are too busy to get involved with troubleshooting others' problems. Fair enough I suppose.

 

[gordonspants]

I am not a plumber by the way. But anyway..

Your boiler is 40kw - that's big.

The way you word things it works as follows - flow from boiler serves at least two primary things - the store, and 22 rads which are themselves possibly zone-valved off into separate zones.

For it to work right, your store must also have a zone valve - so when just the upstairs rads calls for heat, the store doesn't get it first?
When all users are happy, the valves ALL close, except your boiler relies on an autobypass to 'dump' heat when all demand is satisfied. It's a 40kw boiler - how big is this bypass?
My bypass (which I now know we didn't need to fit) is a dinky Honeywell D145 thing - if you have one of those with a couple of standard size radiators hanging off the end, combined with a pump running on trying to get rid of 40kw of heat, there's a possibility that could be the problem. An average 600x1200 radiator wouldn't know where to start with 40kw, neither would a 15mm pipe. A plumber needs to confirm your heatdump is safe and sized right. Not sure, but there may be a way to wire the demand stats via the boiler and then to the zone valve, to get the run-on effect with the valve still open - clever plumber req'd to confirm that!

Or feed the store from the boiler as now, but take everything that uses heat FROM the store (not direct off the boiler) - zoned rads and ufh. There's then no valves between the boiler and it's 'heatdump'. That'd also sort out the overhot rads. Problem there is you may end up with cold showers when your 22 rads and ufh both kick in at once - sounds like your hw setup is a bit limited or undersized?

Having googled the Chelmer website, the 'thermocat' spec says its got its own built-in expansion vessel - yours may have one too? Site also says you can expect 35 l/min of 50 degree hot water, or something like that, I forget. What it doesn't say is how hot the water is to start with, plus how hot the store needs to be to achieve that performance - big, huge, vital omissions! If you can only get that flowrate with 20 degree cold water and a store at 85, you're stuffed. Needs clarifying really.

I reckon you need to really suss out what you have in terms of total system volume, to allow an accurate expansion volume and proper inhibitor dosage to be worked out. Even taking the store out of the equation if it has an expansion vessel built-in, 18 litres doesn't sound very big considering 22 rads etc etc.

The w-b boilers don't have stainless heat exchangers, so wouldn't corrode - not what you want to hear when you have no inhibitor in your system.

Don't get disheartened though - the store will work well - ours does, and I'm sure it saves gas and the life of the boiler, but you need an expert to check it all over - you're right, anyone 'good' will be stacked out even in the credit crunch, and might not fancy re-doing someone elses mistakes.

 

[CMJ]

Thanks for your advice and support, gordonspants. Good to hear from someone who has had experience of similar things.

Your summary is pretty much spot on. The only real difference is that my store actually has 2 zone valves on it rather than one. The upper part of the store provides the DHW store and the lower part supplies the UFH demand. There is apparently some kind of 'baffle' inside the store to restrict the transfer of the hotter water in the upper part to the cooler water in the lower part. Naturally the hot water would rise in any case, but you probably know what I mean.

There are two cylinder stats on the store, one in the upper section and one in the lower section. The upper one is set at between 60 and 70 deg for the DHW and the lower at between 40-50 deg for the UFH.

When the DHW programmer calls for heat, say between the hours of 6am and 8am, the upper zone valve on the store opens, boiler fires up and heats the upper part of the store to the temp set on the upper (DHW) stat. During the heating phase no other heat demand is serviced, irrespective of whether it wants it or not (ie the zone valve on the lower part of the store shuts if open, the UFH pump is switched off no matter what the room stat wants, and all the rad zones are shut if open no matter what the rooms stats want). When the upper section of the store reaches temp the upper zone valve closes and the boiler then continues to provide heat to whatever else might be calling for it at that time (if anything), and opens the relevant zone valves to suit.

The setup really needs the DHW programmer to be ON during periods of heavy hot water usage because when the upper part of the store falls below the set temp on the upper stat (because you are drawing off cold mains water through the DHW coil which becomes your hot water), the boiler's output is diverted immediately to reheating the stored water at the top and thus keeping the flow/temp of hot water constant. When set up correctly is does seem to give me very good results; plentiful supply of hot water at mains pressure for 3 bathrooms all with 'deluge' type showers. It also has a fast recovery time when the hot water supply is finally depleted. Conversely, if the DHW programmer is not set to ON when you're drawing a load of hot water, the supply of hot water is pitiful perhaps not even delivering half a bath-full.

In order to achieve the best hot water flow/temp/recovery Chelmer say the boiler must be set at maximum output i.e. 88 degrees.

All the above is by design. This is how the Chelmer Thermostore (they call it a Thermocat now as you say) works 'out of the box'.

The autobypass we have does exactly as you describe. I think you have probably hit a point with the size of the rads on the bypass circuit, and probably the pipework diameter, although I have to admit that the current setup does seem to work most of the time. I say most of the time because, as I said in my original post, the ABV occasionally does not seem to open (or at least not properly). It may be faulty and I think I should have this replaced with a more heavy duty version regardless. I will get the 'heatdump' assessed by a plumber to ensure it's sufficient.

Your idea about the wiring sounds interesting. It would be great if possible, but I've no idea. Again will have to check this out but I can't imagine who would be able to do this for me as the current wiring looks like something out of an aircraft's wiring loom already! Don't think many plumbers would be able to make a lot of sense of it.

Your other suggestion about taking everything from the store is something I actually wondered about too. The Chelmer installation manual which I have doesn't suggest this, rather it says to do it the way we have already set it up (other rad zones direct from boiler flow/return) but they seem to overlook the hot rad issue which is caused when they say to run the boiler at max! There is no mention of a blending valve either, which is another good suggestion of yours.

I'm not certain whether our store has the built-in expansion you found on their website so I'm sending them an email to find out.

I'm sure this system can and will be great eventually. It's just a case of finding someone who really understands the intricacies of thermal stores and complex controls. It really needs to be set up 100% perfect to get the right results.

Thanks again for your help.

 

[Agile]

As usual I find myself commenting on a situation that i only have very marginal information on.

Firstly the boiler seems very oversized but again we have no information on the whole house heat loss.

22 rads usually mean about 30 kW of heat output but again we done know if they areblargish or smallish.

There is a serious falacy about thermal stores. People seem unable to compare the MI of different products. A condensing boiler is only efficient when delivering a maximum of about 70° flow rate.

Thermal stores are typified for a store temperature of 85°. Put that down ot 70° and a THIRD of their capacity has been lost. That also reduces the heat transfer to DHW as well.

There are a limited number of competent heating engineers in the UK and they are happy to come and advise on heating problems. However they suffer from the stigma of being "plumbers" and no one wants to consider them as experts and pay a return ticket from London and a £300 fee for the day to come to Bristol.

That would be no problem if they were lawyers, accountants or surveyors but as "plumbers" they are not thought of as professionals.

Gorden got a but mixed up about alloy heat exchangers versus stainless. They are more likely to suffer corrosion than stainless and particularly if not inhibited.

Tony

 

[CMJ]

Agile - I don't know how to calculate the house's heat loss unfortunately. It's a Victorian end of terrace, 4 storeys with all external walls insulated with solid wall insulation (50mm of celotex type stuff which is bonded to plasterboard).

I would say the 22 rads are generally average sized. Probably not much help at all. They include 4 large-ish towel rads, 2 very small towel rads, 6 big double rads and the rest mostly 800 x 600 single rads.

I agree entirely with you on this thermal store issue. I thought I was doing the right thing getting this store, and in fact the sales literature even states that it "keeps the boiler in condensing mode". How is that possible if the boiler has to be set to maximum output?! My understanding from reading loads of stuff on this website is that condensing boilers only really work most efficiently at around 55 degrees output. The store needs the upper part of the cylinder to be kept at 70 degrees so how in hell's name would a boiler running at 55 ever manage that! So much misinformation out there, it's easy to make mistakes.

I'm not averse to paying for one of these competent heating engineers to look at this system and work out where it's going wrong. I've never said I don't want to pay for someone - only you said that!

Who's prepared to take at look at it then? I'm open to suggestions.

 

[Agile]

Makers of thermal stores have an uphill task selling their products because they are not mainstream.

They pretend that when heating up they allow the boiler to be condensing, thats with a return of 55°, not flow, but the reality is that most reheat of a store is to top it up and in that case a boiler flow of over 85° means a return of about 70° which is NOT condensing!

Sounds as if your rads are more like 22 kW or less! That makes the boiler even more over powered.

A friend has just bought a four story to refurbish and will have 50-100mm internal insulation and he has calculated the heat loss as just 9.8 kW !!!

D Hailsham will post a link to the heat loss calculator.

Tony