Trouble shooting complex CH problems

[htgeng]

I'm surprised a certain expert thermal stores salesman on this forum has not chimed in to help. Maybe you can get him down to Bristol to fix this mess. Perhaps if we mention the sentence 'take that load of rubbish out and fit an unvented cylinder' he will magically appear.
Also agree that the boiler is way overrated in capacity. If you get cheesed off with WB you might want to look at a decent boiler manufacturer - Atag.

 

[Agile]

I think that the person you refer to as a thermal store salesman has been banned from the forum for giving misleading information!

The reality is that they are not as good as expected for most applications and now that boilers are condensing the situation is worse then before.

The reality is that they are not very compatible with the operating charactistics of condensing boilers.

Tony

 

[gordonspants]

Having been on the Chelmer site again, it's very vague with regard to full performance specs.

From here, I'd say that if you sort your expansion volume out and reduced your boiler flow temp from 88 (my Vaillant doesn't even go that high!!) down to 70, that would solve nearly all your problems - the boiler wouldn't be running flat out, it would be condensing for longer, the radiators wouldn't be able to fry eggs, and possibly even with the suspect bypass as it is now, killing the boiler mid-flow wouldn't cause as much damage/overheating.
But from what you've said, if you turned the boiler down to 70, you'd have about enough hot water for a mug of (fairly cold) tea.

Here I've got a store that uses 70 degree boiler flow, maybe 75 when it's freezing outside, runs 14 rads or thereabouts and does the business with the hot water. It's all down to the plate heat exchanger - if it's spec'd with a 70 degree store in mind, it'll work.
I will (eventually) be able to stick solar, wood stove, gas boiler and elecky immersion into this store - all sources capable of heating 15 rads, doing 30 m2 of ufh and supplying hot water to two showers. There's nothing else out there that can do that - but they get a seriously bad press here from the trade.

I'm not an expert, but the amount of research I did before getting a store was ridiculous. Big thing every time, on every forum I've been through, really seems to be the hot water - if you can size the heat exchanger correctly, and then oversize it even more to deal with winter cold water and a half-depleted store, the store will run at pretty much whatever temperature you want and still heat the water. I'm not knocking your supplier, but if a store needs a boiler at 88 degrees which kicks in immediately and also cuts all other users out to cope, they've economised on the hot water side of things. Hugely.

Doesn't do anything for the credibility of stores punting out stuff that won't work with a modern boiler. I have friends who've just had a house built - ufh throughout, and they've gone with Nuheat for the lot, including their thermal store with internal plate X very similar to the one I originally considered. Works great apparently, loads of hot water, but I still haven't found out exactly what temp their store needs to run at to get a shower in the morning.
If it's 80-odd degrees, the designers are shooting themselves in the foot.
Agile is right - being economical with the facts concerning running temperatures and gas efficiencies isn't a good business plan.

Re the boiler condensing - ideally, return needs to be 50-55, then flow out to the store about 70 for most cond boilers. I still don't 100% understand the delta T, dewpoint etc, but the cooler the flow and return the better basically, something only do-able on a store with a very efficient hot water design.

Re W-Bosch heat exchangers - yep, I can't type!

 

[Agile]

I will (eventually) be able to stick solar, wood stove, gas boiler and elecky immersion into this store - all sources capable of heating 15 rads, doing 30 m2 of ufh and supplying hot water to two showers. There's nothing else out there that can do that - but they get a seriously bad press here from the trade.

I dont think you meant to say the immersion heater would supply 15 rads, at least not continuously!

Thats unless you are having a three phase 60A supply added.

Tony

 

[heatingman]

don't fill the system with artifically softened water, the h/ex's don't like it. Use loads of X100/Fernox inhibitor.

 

[cider]

The long and short of it is loose the thermal store and stick an unvented cylinder in with high recover coil (could make it a solar for possible future use).
I presume underfloor heating has a blending valve already?
If not it could be fitted.
Down rate boiler, fit a bigger exp vsl in the return and your bypass will probably be ok.
I'm north bristol.
email me if you want a chat.

 

[WDIK]

Having been on the Chelmer site again, it's very vague with regard to full performance specs.
!

another doc drivel alias

 

[Agile]

The existing system can be made to work to a degree but the storage capacity will be far less than expected.

Chris Hutt is in Bristol but I have not heard of him for ages. Does anyone know what he is up to?

Tony

 

[Boilerman2]

One of the Big problems with Thermal Stores is the Volume of Water they contain two common problems occur:

1) Inadequate Expansion Capacity (it is possible that yours has some built in) but generally a much larger Exp vessel is needed possibly up to 35 Litres!

2) when dosing the system with inhibitor all too many just read the directions on the Fernox and see that one pack will dose up to 10 rads or what ever, when the reallity of a 250 Ltr Thermal store 4 or 5 packs are actually required!!

 

[Norcon]

Another problem is a scaled heat exchanger. Isn't Bristol a hard water area?
88c and hard water is hardly a good partnership with what I think is an immersed phe inside the thermastore which will be cooked up like a kipper.
Best bet is rip the SB out and fit a UV cylinder.

 

[CMJ]

Since my last post a Worcester Bosch engineer has been out and replaced the HE (again) and so at least the system is functioning without the need for the 5am daily top-up ritual to which I had become accustomed!

I’ve also been in touch with Chelmer once more and I have to say this time I seem to have found the right person to speak to (or rather email). A very helpful chap called Alex who is their Operations Manager and has been able to answer all of my questions so far. Here’s an update on some of the key points:

1. I actually have a 300L Dual Thermostore (they now call it a Thermocat) not a 280L as originally thought.
2. The store contains its own expansion ‘bubble’ at the top of the cylinder which accounts for all the expansion of the store’s water content (i.e. 300L) but not for any other parts of the system such as rads, UFH or pipework/primaries etc. I think he said the built-in expansion is about 28L. He confirmed that I need a sufficient external expansion vessel for the rest of the system (which I pretty much knew).
3. Apparently I do not need to run my boiler at maximum output, contrary to the advice given in their installation manual! Alex suggests I can run it at whatever output I wish provided that it is at least 5 degrees above the stat setting on the cylinder. I’m not 100% convinced by this as I would have thought the DHW recovery would be compromised significantly, but I’m going to experiment.
4. Sufficient inhibitor for the entire system (store, rads, UFH and pipes etc) must be used. I very much suspect this is where the original installer cocked things up to start with, probably just following the info on the bottle for a ‘standard system’ rather than calculating the proper dosage, as Boilerman2 has suggested.
5. He recommends using softened water to fill the system if it’s available BUT says that sufficient dosage of inhibitor MUST be used. I have read on Setinel’s website that X100 is designed to work with softened water. Any experience of this?
6. With regards to the condensing boiler issue, he says “The thermostore is designed to help keep the boiler in condensing mode by supplying a return temperature back to the boiler of no greater than 50°C (hence why the boiler return pipe is at the very bottom). This is achievable with the thermal store using flow temperatures in excess of 65°C”. I’m not entirely convinced that the return IS always less than 50 degrees, so I’m going to take some temp readings at various times and see what is happening.

With all that in mind I’ve now done the following:

1. Have calculated or obtained from the manufacturer the volume of water (excluding store) as follows: Rads (110L), UFH (34L). Have estimated pipework to be 30L water volume. Therefore total = 175L making my current 18L vessel seem sufficient, which was a surprise to me. I'm still wondering whether it's located at the correct point in the system though; it's currently AFTER the auto bypass valve (itself on the flow) rather than on the return. Appreciate any of your thoughts.
2. Based on the above the total system water content (incl store) is 474 litres. Sentinel advise dosage at 1 litre for every 70L of system water, therefore a whopping 7 litres (ish) of X100 required! Chelmer provide instructions on how to add the inhibitor into the store, but would adding the whole lot to the store mean that the rad circuits don’t get any? Would it be a good idea to split the dosage between the store and direct into the rads?
3. For the time being I’ve set my store at 65 and the boiler output at 75 and will try it for a few days.

Now a new issue comes to my attention which is troubling me; two of the three rad zones (which are run directly from the boiler primary flow) do not have zone valves. I thought they did but in fact on digging around in the cupboard where it’s all fitted there is a separate pump for each of these two zones instead of a zone valve. They are wired into a wiring centre with some relays (?).

I have vague recollections of the installer originally fitting 3 zone valves (i.e. one for each rad circuit) but then deciding that more pumps were needed to circulate the flow to other floors, thus replacing two of the zone valves with pumps. I therefore have 1 main pump on the flow (under the boiler) plus a pump each for two of the three rad zones, plus another pump (or even 2 I think?) for the 2 UFH zones. The 3rd rad zone has a zone valve.

Why is this troubling me? Well, the pumps clearly don’t ‘close’ the rad circuits off! This has only just come to light since I’ve opened up all the TRVs to max for the boiler engineer after he part drained the system to replace the HE (he said a good idea to ensure system circulates and all air works its way out?). I’ve noticed now that ALL the rads on 2 floors warm up even when the room stat is not calling for heat! This is a bit ridiculous isn’t it? This means that when my boiler is trying with all its might to heat the store, some of the heat is being ‘lost’ into rad circuits that do not want it. An utter waste of energy! To be honest, I’ve noticed a couple of rads getting warm at unusual times in the past (the ones on the landings with no TRVs) but I’ve always put that down to them being on a bypass circuit. Turns out I’m wrong – they were being heated when the store is calling for heat for either the DHW or UFH.

What should I get done about this? Do I really need two extra pumps, themselves costing money to run? Could the installer not have upgraded the main pump to cope? I’m sure it all worked fine when 3 zone valves were fitted, I visited plenty of times when the heating was running during the refurb. If I do need 2 extra pumps, can you get ones that close a valve or something when they turn off? I’m sorry I’m such a novice at all this.

Some responses to points made by others (thanks all for your input – greatly appreciated):

Gordon – from what you’ve outlined it would appear the main area of compromise in my store is the heat exchanger. The Chelmer store “incorporates a patented high performance tristage monopath coil heat exchanger” which I assume is not a plate heat exchanger. Is this the source of my DHW problems?

I haven’t asked Chelmer about the idea of a blending valve for the rad circuits, but I think this could be a good idea and I’m going to investigate further. I presume it would work the same way as the UFH blending valve, chucking flow water up the return when the valve is satisfied? Do I foresee another problem with the return becoming too hot for the condensing process to work again?

With regards to the performance figures for this store, I have to agree the figures on the Chelmer website are vague to say the least. I’m going to ask Alex for more detail in my next email.

I don’t have a Magnaclean (!) but from reading all about them on this forum I’m going to get one fitted ASAP. I’ve no idea why the original installer would have skimped on something so obvious given the complexity and cost of this system. I wouldn’t have baulked at another £150-£300 for the magnaclean installation. I’ve also read about the Spirovents and wonder whether there is merit in fitting BOTH a Maganaclean and a Spirovent? The attraction of the Spirovent being the elimination of air which, from reading the Chelmer manual, seems can be a significant cause of loss of performance of the DHW. They say that to eliminate this the store should be vented 2 or 3 times over a 2 months period after the initial commissioning.

I’m going to get a Powerflush done at the same time as fitting a Magnaclean.

Bristol is indeed a (fairly) hard water area, hence we had the water softener fitted. It's a fairly hefty device called a Water Boss Mega Flow.

Ripping the store out and replacing with an unvented cylinder, whilst being desirable as it would satisfy my craving for tons of DHW, is not really an option for me. Firstly I don't have the money. Secondly I would waste money already spent by binning this thing. Thirdly I would need to take down and rebuild the cupboard/small room into which the store is fitted as it was partially built around it. I know, I know, stupid idea. Add to this the disruption it would cause (I’ve got 2 small children and the store is at the top of the house) and it doesn’t sound very appealing. That’s without mentioning the fact that I actually had some input into the concept of having a thermal store at the outset, so I feel I owe it to myself to make this damn thing work to its maximum capability. I think if I’d actually gone ahead with the original plan to have the solar hot water I would have felt a little less disappointed, despite these problems still existing.

One thing I have yet to do is attempt to calculate the heat loss of the building and the heat output of the rads and UFH etc to see how the installer came up with the idea of fitting a 40KW boiler. As a side note, the Worcester engineer didn’t seem to think it was too big for the property size, but that doesn’t necessarily mean anything.

My and my plumber’s (when I find a good one!) To-Do list and things to research further are:

1. Powerflush
2. Maganaclean and/or Spirovent
3. Fill with correct dosage of X100
4. Obtain more detailed figures from Chelmer on the store’s performance
5. Calculate the boiler size from rad heat output and property heat loss etc.
6. Take my own temp readings of the return to check if below 55.
7. Have the auto bypass valve and bypass circuit checked out for both operation and sizing.
8. Do something about the rad pumps that do not close off the circuits.
9. Confirm expansion vessel is adequate and is correctly located in the system.

Apologies once again for the very long post but I do appreciate everyone’s time and input.

 

[gordonspants]

Having been on the Chelmer site again, it's very vague with regard to full performance specs.
!

another doc drivel alias

Funnily enough, that's what was said when I posted about fitting a store in my house last year. Actually, not that funny, or helpful, but nice try anyway.
If you click on my profile, or name, or something, you can get thru eventually to my album, with pics with my boiler and store. It does exist. Really.

Main reasons for ME choosing a thermal store as opposed to a hot water cylinder....
1 – I wanted solar, wood burner and gas - all able to heat rads AND hot water.
2 - no loft or room for header tanks etc - so I had a straight choice between an unvented cylinder or what I chose...
3 - hey, it's different, it’s the future, it’s rubbish, it’s 'not as good as an unvented cylinder', whatever. But it works great.
4 – excellent hot water – biiiiig shower with rain effect head and bodyjets.
5 - loads cheaper than a quote I got for an OSO unvented and accumulator package. And I mean LOADS. I’ve got secondhand solar, a 10 kw stove, a 300l store and a new Vaillant condenser for the same £. No contest.

CMJ - as you're not going to take the store out, you need to get it to work properly.
‘Chucking in an unvented’ may have been a better option to start with, as you don’t need the multiple energy source capabilities of a store, but ufh companies (eg nuheat again) DO use thermal stores in their installs – there must be a reason for that?
As I've said, I'm not a plumber, but feel 'qualified' to answer on the basis that I've got a store. Nothing more than that.

So, your points..from a layman’s point of view…

1 and 2 – if the store has it’s own ‘bubble’ is it like a megaflop? – they can ‘lose’ their bubble and have to it get re-charged with a bicycle pump I believe. If yours can lose the air, you need expansion volume elsewhere to compensate and make everything safe.

3 – you need to nail the Chelmer guy down and get actual, proper performance figures.
That would be cold water temp in vs hot water temp out at x degrees at y litres a minute based on store temperatures of x,y and z degrees. Without knowing the temperature rise per litres a minute you can achieve at various store temps, you don’t know if you can turn your boiler down.
You’ve got, and I quote, ‘a patented high performance tristage monopath coil heat exchanger’. It sounds technical, but it’s probably a ribbed coil of copper pipe.
With a plate heat exchanger you can be within a few degrees of your desired water temp if it’s sized right – I can shower in the summer in, what, 45 degree water with a store at 50-55.
If I got a bigger heat exchanger, the theory is I could still do that with mains water near freezing.
That’s theory anyway – as it stands I need the store over 70 in the dead of winter. Very generally, coils are crap in comparison – but only from what I’ve read.
If your coil is as spangly and clever as the name suggests, it should be pretty good.
If not, you might have to look at altering things – have a look at nuheat or dps websites to see their plate heat exchanger diagrams – you might be able to retro fit an external one with a shunt pump and flowswitch using the existing tappings on your store – a plumber needs to look at that and advise. A more knowledgeable one obviously, not the one you’ve had.

6 – I have temp gauges all over mine, total of six I think, so we can see what’s going on. We thought that fault-finding would be a real p.i.t.a with no information.

Re the pumps and valves – yes, I reckon each zone or user should have a valve! Whether you need one pump per zone valve, or just the one pump that then tees off to all the zone valves I don’t know – you need a plumber to look at the loads and size the pump(s) correctly.
I have one pump that does two zones (will eventually be four zones here), each zone has it’s own 2 port valve. So all users have the one pump, plus I have one built-in in the boiler obviously.
If your boiler is heating your rads when it’s supposed to be doing the store, no wonder the hot water is marginal.

Magnaclean – yes, or spiroclean, probably the same thing. Something anyway!
Inhibitor – loads! If you’re in a hard water area (I’m not) scale will be a problem as said above. Whether inhibitor prevents scale I don’t know – but it’s something that needs looking at because with the higher temps a store runs at compared to a cylinder, scale buildup and reduction in performance will be quicker, especially around the hot water generation bits. Don’t know much about scale, just what I’ve read.

Don’t rip it out – it just needs someone knowledgeable to work on it – that’s the battle, finding someone. My guy is nuheat-approved – might be worth asking them if they have anyone good local to you.

 

[Agile]

The sad fact is that most manufacturers have virtually no serious test data.

A different facet but most manufacturers have NO information on the noise level their boilers produce.

The odd one or two that do quote something are not even quoting a level properly anyway. ( e.g. the boiler produces 42 dBA of noise )

I have just come back from a boiler epair that has been visited by Homeserve, Vaillant and a local plumber! None of thew could/would repair the boiler or even seemed to know what was wrong. The local plumber was totally abusive to be but thats typical of an ignorant plumber who knows that he does not have any skills. The owners saw that I was the one that repaired the boiler and I did not need to touch what the plumber said was wrong.

Tony

 

[Drain]

I have just stumbled on this forum after ordering a Chelmer System 2000 UFH system plus 280L Thermocat thermal store. I have independently procured a Grant VTX 15/24 condensing boiler. I did my research before this forum was started and could not find much in the way of neutral assessments so I made my choice based on technical descriptions and a discussion with my plumber. Eventually I narrowed my shortlist to Chelmer and NuHeat. Two things tipped me in favour of Chelmer: 1. my plumber thought the aluminium layered pipe would be quicker and easier to lay, and 2. the Thermocat appears to be the only thermal store which combines internal stratification with two separately controllable hot water inputs, plus two corresponding thermostats. The rationale is that this "dual" system makes it possible to drive the DHW heat exchanger and the UFH coils at their respective ideal output temperatures while demanding targeted primary HW from the boiler in efficient infrequent (condensing) cycles. Chelmer recommends that the upper stat is set to 65-75C; this will output DHW a few degrees less which is then capped to 53C with a preset mixing valve. Meanwhile at the bottom of the tank the lower stat should be set to 35-55C to heat the captive UFH water accordingly. This apparently will return <=40C to the boiler to maintain condensing. Well I was convinced anyway!
Looking at the above discussions I can see why the Thermocat may not be so effective for radiators.
So far I have paid the deposit and have received detailed drawings and documentation which have been really impressive. And Chelmer was very helpful about making detailed changes.
I will keep this forum posted with my progress after the system has been delivered in February.

 

[Norcon]

Chelmer state amongst other things that the efficiency of the thermcat is due to the buffering that the extra volume provides thus reducing boiler cycling.
It may not reduce boiler cycling though and may in fact increase it!

What happens is, the boiler heats the store. The heating comes on and starts to empty the store.
The boiler fires at the request of the thermostat positioned on the store.
The cold water from the heating system goes to the bottom of the store and is immediately cycled through the boiler.
Whilst both are running, cold/cool water returning from the heating system will go straight to the boiler. It won't see the buffer tank at all.

So, there's little point having one!

If the boiler is making more heat than the heating system can use, the temperature in the store starts to climb. The return to the boiler becomes a mixture of the cool water returning from the heating system and the warmer water in the tank. So the boiler works at an increasingly high temperature.
Which leads to inefficiency and may cycle the boiler.

If the water from the heating system goes straight to the boiler return with no interference from the store , it will always be the coolest possible water that could be returned to the boiler , which will work most efficiently.