Condensing system boiler options in an S-plan?

[ms1012]

I've recently received several quotes to replace my current system boiler as it repeatedly failed over the past winter. 4 bedroom detached house, system boiler in the garage, megaflo cylinder upstairs. Online heat calculator suggests 14.5 kW heating required.

I received quotes suggesting a Vaillant ecotec plus 630 or a Worcester Bosch 30CDi. None of the companies supplying quotes suggested an upgrade of existing controls (Myson 2 channel timer to control heat/hot water, and a Honeywell CM907 room stat).

I'm concerned that for either of these quotes, the boiler will not be operating optimally. I suggested a vr 65 control center with appropriate weather control / room stat options to the person quoting for the Vaillant, but he dismissed it suggesting it's equivalent to what I have already, just vaillant branded (I thought it would assist with modulating / condensing?).

Am I just being taken in by all the marketing spiel from these companies, and is my current setup just fine for taking advantage of a condensing boiler? Is there something else I should be considering? I tried to find a local (Glasgow) Remeha installer but no luck so far. Should I consider Viessmann as well?

One final thought, current gas supply to the old boiler is 15mm (or less) with the gas hob supply taken from the same feed (hob flame drops when boiler kicks in). I feel this should be upgraded, am I right in thinking this?

 

[onlyfitidealboilers]

did you inform the installer about this? as it is at risk and you should not use it.

 

[ms1012]

did you inform the installer about this? as it is at risk and you should not use it.

The current setup was fitted at the time the house was built, 5 or 6 years ago so I guess the building inspector was happy to sign off on it. I bought the property recently but from what I've seen so far, the builders were a right bunch of cowboys. I really would feel better if a new supply was run, but I guess if it tests ok... We may also replace the gas hob with an electric one in the future, which would leave the boiler as the only gas appliance.

 

[UpgradeME]

None of the companies supplying quotes suggested an upgrade of existing controls (Myson 2 channel timer to control heat/hot water, and a Honeywell CM907 room stat).

I'm concerned that for either of these quotes, the boiler will not be operating optimally. I suggested a vr 65 control center with appropriate weather control / room stat options to the person quoting for the Vaillant, but he dismissed it suggesting it's equivalent to what I have already, just vaillant branded (I thought it would assist with modulating / condensing?).

I'm looking to upgrade the controls on my Vaillant boiler and I'm currently investigating the options (see my thread on here). So far, I believe you are correct in that without the Vaillant controls, you won't get the modulating efficiences from the boiler.

So, I believe the VRT392 modulates based on internal room temperature and the VRC430 does it based on external temp (and costs £50-100 more for the control), your existing controls will not modulate the output AFAIK.

The only thing I'm not 100% sure on is if the Vaillant boilers modulate anyway based on the return temp, regardless of what controls you have? (I can't find this mentioned anywhere in their doc's but have seen it mentioned 'in general' when talking about boiler modulation.)

 

[ms1012]

Hi UpgradeME, I'm glad I'm not the only one stumped by this. This has to be a very common problem? Do people really just not care about boiler efficiencies?

I too assume the boiler will do some sort of modulation on return temps to try and keep it condensing, but with the system boiler heating the hot water it has to reach 65 degrees or whatever is required to keep the water healthy. Does the automatic modulation (if any) basically try and keep the boiler output at the desired temp (presumably set by a boiler thermostat?) by modulating burner output rather than cycling on/off?

I believe that if you use the VR 65 control center the Vaillant can start using seperate hot water / heating temps (including when heating hot water to ignore weather compensation and just go flat-out to heat the big megaflo), but I'm completely at a loss about details, especially with the guy recommending the Vaillant boiler stating that the vr 65 is just the same as my current (on/off) controls?

 

[ms1012]

I guess my other limation is with the Megaflo and VR10 NTC which don't seem to go together well. The vr 65 docs suggest that VR10 NTC is optional, so I guess could live without it for now? Could decide to rip it out in the future and install Vaillant's own alternative.

 

[UpgradeME]

I too assume the boiler will do some sort of modulation on return temps to try and keep it condensing, but with the system boiler heating the hot water it has to reach 65 degrees or whatever is required to keep the water healthy. Does the automatic modulation (if any) basically try and keep the boiler output at the desired temp (presumably set by a boiler thermostat?) by modulating burner output rather than cycling on/off?

I'm guessing... but.. I think the boiler will modulate the burner based on set boiler temperature and the return temp to help condensing.

I think the VRT392 add's to this by modulating the burner output based on the current and set room temp. So as it approaches the room temp and after it has reached room temp, the boiler modulates the temp down which increases condensing = higher efficency.

The VRC430 add's outside temperature into the equation, see this link for a good explanation of how that works! http://bit.ly/gEHtll

I believe that if you use the VR 65 control center the Vaillant can start using seperate hot water / heating temps (including when heating hot water to ignore weather compensation and just go flat-out to heat the big megaflo), but I'm completely at a loss about details, especially with the guy recommending the Vaillant boiler stating that the vr 65 is just the same as my current (on/off) controls?

The VR65 basically a "Control Centre" for the valves and HW temperature, it sends/receives the digital eBUS signals from the boiler and operates your Zone Values and HW temp. If you use the (included) VR10 NTC instead of a normal 230v tank stat ('technically' it's designed for Vaillant tanks but can be fitted to others!) you can have seperate HW/CH temp outputs so again the boiler can be more efficient.

I don't think many people understand it to be honest, even the installers. It doesn't help with the information on Vaillant's site being rather limited and out of date (they still mention their old controls instead of the new 392 in all comparrisons )

 

[ms1012]

I'll see if I can get some alternative Vaillant installers to come round for a quote, see if I can find one who's done a vr 65 install.

I guess Worcester Bosch doesn't have anything equivalent? Their own intelligent controls all state not compatible with S/Y plan systems?

 

[picasso]

you both seem to have sussed out what the vr65 can and cannot do, its a better option than simple on/off controls, why has the installers quoted for such a big boiler? if you reckon the heat load is around 14kw you should be looking for an 18kw boiler, cant see the sense in a 30kw boiler.

 

[D_Hailsham]

upgrade of existing controls (Myson 2 channel timer to control heat/hot water, and a Honeywell CM907 room stat).

I suggested a vr 65 control center with appropriate weather control / room stat options to the person quoting for the Vaillant, but he dismissed it suggesting it's equivalent to what I have already, just vaillant branded (I thought it would assist with modulating / condensing?).

The aim of the CM907 is to maintain the room temperature to within half a degree of the required temperature and to prevent overshoot when the house first warms up. It has nothing to do with controlling the modulation of the boiler. The only way you will do this is by using a controller which directly controls the modulation.

I tried to find a local (Glasgow) Remeha installer but no luck so far.

Give Remeha a call. They will tell you who their distributor is in Glasgow. The distributor will then give you the names of several installers. It's a long way round, but the distributors will know who has had more experience.

If you are wanting to install an S plan, you can't have weather compensation - unless you time the HW so it never heats up when the central heating is on. The reason for this is simple: HW needs the boiler to run at more than the desired HW temperature and preferably at max temperature to heat the water. Weather comp can have the circulating water at only 40 degrees.

The way this is often overcome is to use a diverter valve, normally open to the CH. When HW is required the diverter closes to CH and opens to HW. At the same time the boiler is automatically cranked up to max output. It's identical to the way a combi boiler works.

 

[picasso]

the vr65 allows an s plan to be used with vaillants modulating controls (including weather compensation) go on shoot me down

 

[ms1012]

I'm even more confused now....

Thought I'd get the information straight from Vaillant, emailed them for confirmation. Got the following response:

Your installer is correct whether Vaillant controls with a VR 65 or external controls are used it will not affect the efficiency of the boiler or the heating system.

So now the Vaillant technical support people are saying their supposedly advanced controls offer no benefits over a simple on/off roomstat + timer combo?

 

[Agile]

Blind leading the blind comes to mind!

Those controls do give a SMALL improvement in efficiency depending on how they are used. Perhaps about 5%.

I am yet again very disapointed that your installers have no idea of how to size a boiler to match the heating load! Some of my trade colleagues think that I am too quick to slate the nupty installers we see written about who so often seriously oversize boilers. They should have gone on an efficiency course in the last few years where this was taught.

Customers are often to blame as well as they usually just look for the cheapest installation and not the most competent installer.

Tony

 

[ms1012]

I do get the feeling I'm over-thinking this all. A condensing boiler that's not condensing should be as efficient as a regular boiler, right? So that's 80% instead of 90%?

So all this fancy controls logic etc is trying to ensure that it's spending more time at 90% rather than 80%? That puts a bit of perspective on it.

Thinking logically, if a boiler were to be 100% effective, the only way to save money would be to lower temps, or decrease how often the boiler is on. Both of which would equate to a drop in temps and thus comfort level.

So when someone says that weather compensation improves efficiency say 20%, do they actually mean you get a 20% better chance of running at 90% instead of 80%?

Out of the 2 boilers (Worcester Bosch CDi30 vs Vaillant ecoTEC plus 630), is one preferable over the other? The WB has an alu heat exchanger, but will modulate down to 7kW or so instead of 10 on the Vaillant. Should I consider the Vaillant 624 instead as it's less oversized? (current timer settings ensure that I never run hot water at the same time as heating... timer closes heating valve at 1am and gives the hot water a 3 hour window to heat up using 100% of boiler output).

 

[Agile]

I do get the feeling I'm over-thinking this all.

So when someone says that weather compensation improves efficiency say 20%, do they actually mean you get a 20% better chance of running at 90% instead of 80%?

I think that you are overthinking and that worries me because you expect to know more than the experts ( which does not include the nupties who oversize boilers ). Obviously you are intellectually superior to anyone who works in the heating industry. Just be aware that not boiler engineers are nupties though.

You dont say who told you that weather comp saves 20%.

I suggested about 5% if its used properly.

Probably better if I leave you to continue chatting to Upgrade ME as you seem to prefer to ignore my advice!

Tony