Underfloor Heating and Flowswitch Question

[alaska]

I have a combi boiler. The CH is a closed system and pressure is maintained. I have one room with underfloor heating that was extended off the existing CH circuit. There is a booster pump fitted to pump the hot water round the narrow diameter pipe work. Up on the boiler located at the mains inlet to the boiler is a flow switch. I'm struggling to understand the purpose of the flowswitch.

So far I think I have established that when I turn on a hot water tap the flow switch turns off the underfloor heating pump. Does this sound about right? Could it be to stop the radiators running cold, whilst I draw domestic hot water? - so basically shutting off the underfloor heating prioritising the radiators.

If the CH is closed loop, why would I need to shut the pump down when drawing domestic hot water from outside the closed loop.

Appreciate any advice.

 

[stevetheplumber]

I have a combi boiler. The CH is a closed system and pressure is maintained. I have one room with underfloor heating that was extended off the existing CH circuit. There is a booster pump fitted to pump the hot water round the narrow diameter pipe work. Up on the boiler located at the mains inlet to the boiler is a flow switch. I'm struggling to understand the purpose of the flowswitch.

So far I think I have established that when I turn on a hot water tap the flow switch turns off the underfloor heating pump. Does this sound about right? Could it be to stop the radiators running cold, whilst I draw domestic hot water? - so basically shutting off the underfloor heating prioritising the radiators.

If the CH is closed loop, why would I need to shut the pump down when drawing domestic hot water from outside the closed loop.

Appreciate any advice.

when the combi goes to hot water it shuts the circuit to heating so your ufh pump would be either pimping against a blocked pipe or drawing water away from the hot water heating circuit inside the boiler
to overcome this the flow switch turns of the ufh pump
are there any identifying marks on the flowswitc as im looking for a flowswitch that swithces to of when the water flows ?or do you have a photo of it ?

 

[Bernie2]

Yes agree with Steve. Combis give priority to hot water and shut the heating side off.

Its a valve inside the combi itself, that changes flow from the heating to the hot water.

Obviously the pump for the UFH is not part of the combi, so they put a flow switch in the UFH pump supply that tells the pump to shut down when it detects no flow, as the combi has switched from central heating to hot water. Once it detects its changed back again the flow switch turns the pump back on. That is the way it would appear to work.

 

[alaska]

Thanks for the replies. I'll post a photo of the switch tomorrow.

Sorry just one more question. If I was having a problem that essentially meant that maybe a couple of times out of every ten times I turn a tap to try and get domestic hot water the boiler doesn't fire up, can I eliminate that this is anything to do with the underfloor heating and more so the flow switch. I think I can since the flow switch has no direct connection to the boiler and surely if it was faulty it would just affect the UFH pump and nothing else?

The reason i ask is I am lined up to get a Ferolli Engineer to come out to do a service/fix on the boiler on a fixed price "we'll fix it no matter what" basis. Now I know they will only look at the boiler and not any peripheral modifications, but I don't want them not fixing the boiler and suggesting the fault lies elsewhere? The only other modification is that we have fitted a wireless thermostat control to the boiler - but I figure this is fairly common?

Again thanks - photo to follow of flow switch it was from Novomec Group.

 

[stevetheplumber]

Thanks for the replies. I'll post a photo of the switch tomorrow.

Sorry just one more question. If I was having a problem that essentially meant that maybe a couple of times out of every ten times I turn a tap to try and get domestic hot water the boiler doesn't fire up, can I eliminate that this is anything to do with the underfloor heating and more so the flow switch. I think I can since the flow switch has no direct connection to the boiler and surely if it was faulty it would just affect the UFH pump and nothing else?

The reason i ask is I am lined up to get a Ferolli Engineer to come out to do a service/fix on the boiler on a fixed price "we'll fix it no matter what" basis. Now I know they will only look at the boiler and not any peripheral modifications, but I don't want them not fixing the boiler and suggesting the fault lies elsewhere? The only other modification is that we have fitted a wireless thermostat control to the boiler - but I figure this is fairly common?

Again thanks - photo to follow of flow switch it was from Novomec Group.

what you said sound correct cant see anyreason the flowswitc does anything more than turn of the ufh pump and should have no bearing on hot water operation sounds like a divertor valve or diphram problem

 

[alaska]

Photos as promised