Advice on thermostat options for underfloor heating with Intergas combi

[Razor900]

Pretty sure it's a combi

And what difference will that make?

 

[trojanhawrs]

And what difference will that make?

It can't call for heating and hot water

 

[Razor900]

It can't call for heating and hot water

I never said it could. But.....

The Intergas boiler uses a bithermic heat exchanger meaning it has two sets of pipework, one for the dhw and one for the heating.

With the setup the OP has when there is a call for heating it will go to the boiler and UFH pump. If the boiler is having a call for hot water at the same time it will ignore the heating demand.

However the UFH pump on the manifold will still run and it will create a parasitic flow across the boilers flow and return which will scavenge heat from the larger heating coil in the hex and cause poor hot water performance.

I was the senior engineer for Intergas in the UK for 5 years and have seen it happen many times but I will let you off as you weren't aware of this particular boilers unique properties. A more conventional combi would not have this issue.

BTW Just to make the OP re-evaluate how complicated he thinks his system is. This one I installed serves 250 square metres of UFH and 22 rads with priority domestic hot water, weather comp and Opentherm...

 

[trojanhawrs]

I never said it could. But.....

The Intergas boiler uses a bithermic heat exchanger meaning it has two sets of pipework, one for the dhw and one for the heating.

With the setup the OP has when there is a call for heating it will go to the boiler and UFH pump. If the boiler is having a call for hot water at the same time it will ignore the heating demand.

However the UFH pump on the manifold will still run and it will create a parasitic flow across the boilers flow and return which will scavenge heat from the larger heating coil in the hex and cause poor hot water performance.

I was the senior engineer for Intergas in the UK for 5 years and have seen it happen many times but I will let you off as you weren't aware of this particular boilers unique properties. A more conventional combi would not have this issue.

BTW Just to make the OP re-evaluate how complicated he thinks his system is. This one I installed serves 250 square metres of UFH and 22 rads with priority domestic hot water, weather comp and Opentherm...

Thanks for the detailed response, that's interesting. I remember hearing they didn't use a diverter valve but didn't put much thought into how that worked.

 

[phil63]

It's a HRE 24/18 Intergas Combi boiler; the flooring is 15mm engineered oak of some sort. There are no radiators, it's a ground floor victorian terrace flat, with newly installed sub-concrete UFH.
Razor900, are you saying, like Muggles earlier, that the second pump is not needed, overkill, or even a bad idea for functional reasons? Do you think the current set-up can be reconfigured without too much grief to work as you suggest? Is there any conceivable reason they would have put an extra pump in the system? I'm going to head over and try and talk to the builder tomorrow, so I want to be ready for any spurious arguments or waffle..

 

[Razor900]

You are massively overcomplicating things.

Run the UFH manifold directly from the boiler with no blending valve/pump on the manifold or outside sensor. If you want to zone each area just do it with actuators and ordinary room stats

Then set the boiler flow temp to 40 degrees and lock it so no one can accidentally alter it.

No advantage whatsoever to using OT or WC in this situation

I already said what needs doing in my first post.

Basically flow goes into top rail of manifold and return to the bottom and that's it you dont need anything else.

The boiler flow temperature can be locked so it won't go above 45 degrees (or whatever the flooring manufacturer specifies) and you save money and hassle

 

[phil63]

I never said it could. But.....

The Intergas boiler uses a bithermic heat exchanger meaning it has two sets of pipework, one for the dhw and one for the heating.

With the setup the OP has when there is a call for heating it will go to the boiler and UFH pump. If the boiler is having a call for hot water at the same time it will ignore the heating demand.

However the UFH pump on the manifold will still run and it will create a parasitic flow across the boilers flow and return which will scavenge heat from the larger heating coil in the hex and cause poor hot water performance.

I was the senior engineer for Intergas in the UK for 5 years and have seen it happen many times but I will let you off as you weren't aware of this particular boilers unique properties. A more conventional combi would not have this issue.

BTW Just to make the OP re-evaluate how complicated he thinks his system is. This one I installed serves 250 square metres of UFH and 22 rads with priority domestic hot water, weather comp and Opentherm...

View attachment 397724

Yeah, that is a pretty scary sight to me at the moment.... So the fact it is an Intergas, and not a Vaillant is critical: I asked them to go for Intergas (possibly rather than their preferred WB or Vaillant..) so he'll probably turn it back on me.. Anyway, the same question arises; should I get them to remove that pump and blend valve if possible? Can it not run at a low enough temperature without a blend valve? (I thought the idea was to run a condensing boiler as low as possible anyway). I don't want to cause him to throw a hissy and disappear for another few weeks. Is there such a thing as a basic schematic showing the ideal set-up with an Intergas combi, that I can give to him? Along with the reasons you've given me, it would help me push the point home.

 

[phil63]

I already said what needs doing in my first post.

Basically flow goes into top rail of manifold and return to the bottom and that's it you dont need anything else.

The boiler flow temperature can be locked so it won't go above 45 degrees (or whatever the flooring manufacturer specifies) and you save money and hassle

I finally had a response from the builder/plumber today! Many thanks to you Razor900, I basically quoted what you said (I may have also promoted you to current 'Head of Intergas Research and Development'). He doesn't concede that the set-up was excessive for 'normal' boilers.. but does concede your point about the parasitic flow, and as it was me that insisted on an Intergas, I guess that's partly on me.. anyway, he lists the following list of mods basically along the lines you suggested:

1. Remove the manifold pump & blending valve, pipe boiler flow to the top rail and return from the bottom rail.
2. Lock the boiler CH flow temperature at 40–45 °C (per floor spec) so nobody can crank it up later.
3. Add a check/non-return to stop any ghost flow when there’s a DHW call, and make sure the UFH call is wired to the boiler correctly.
4. Keep the wiring centre/actuators as they are for zoning; consider a strap-on limit stat on the flow rail for belt-and-braces protection.
5. Fit the scale inhibitor and the shock arrestor on the cold feed to the boiler — good call, especially with that tight lower push-fit.

He mentions a check valve to stop 'ghost flow' - I'm not sure what this is, d'you think it's necessary? Also he mentions a strap-on limit stat, which might be a good idea.
Thanks again
Phil

 

[Razor900]

He sounds a decent guy to be honest and they are quite sensible suggestions.

As the pipework goes down directly under the boiler there is no need for a check valve it would only be the pump on the heating manifold that could cause issues and that's being removed. You would only get gravity circulation if the pipes went up from the boiler.

As for limiting the flow temp to the manifold by fitting a thermal cut out again a good call but not needed in this case. Parameter 5. (5 dot) controls the maximum flow temperature that the user can select. If he sets it to say 40 degrees it will not be possible to turn the boiler thermostat up higher than that.

 

[phil63]

Thanks Razor900 that’s great; I’ll get him to do as you suggest .. hopefully it’s less than a day’s extra work.