Why One Manual Valve?

[MartinW]

Hi

I have had a smart system installed to control my boiler. This consists of a control unit attached to the boiler, Smart TRV's on all radiators except the living room which has a smart room thermostat (manual valve on living room rad).

My question is, why must I have a manual valve on the rad in the room with the room thermostat? I get that building regs state this but it means that whenever I want to heat, say, just the bathroom, the living room also has to heat up because it has the manual valve, so wasting money.

 

[steadyon]

Because if you have a thermostatic radiator valve on the radiator in the room with the room thermostat, the two thermostats will fight each other. TRV says "hot enough" so room stat will never reach temperature. Or room stat says "hot enough" and room doesn't warm.

 

[MartinW]

But with a smart system does the room thermostat doesn't directly control the rad in that room? Because if the rooms with the TRVs still need heat to get to their independent set temp the boiler still fires and will continue heating the room with the manual valve anyway regardless?

 

[fronty]

How smart is your system? Does the room stat control when the boiler fires based on the temperature in the living room? If the living room gets up to temperature does the boiler shut down even if there are other rooms that haven't reached their set points yet?

There might be another reason why you have to have a manual valve on the living room rad and that is so that it can act as a bypass for when all the other TRVs are shut. If the living room also had a TRV that was shut then the pump will be pushing against all the closed TRVs and God knows what'll happen as the water can't go anywhere.

I've got Evohome in my house so the living room rad has a smart TRV but I have no TRV on my bathroom radiator, so that acts as the bypass in my house, it means it's always on but for the bathroom that's fine.

 

[MartinW]

How smart is your system? Does the room stat control when the boiler fires based on the temperature in the living room? If the living room gets up to temperature does the boiler shut down even if there are other rooms that haven't reached their set points yet?

There might be another reason why you have to have a manual valve on the living room rad and that is so that it can act as a bypass for when all the other TRVs are shut. If the living room also had a TRV that was shut then the pump will be pushing against all the closed TRVs and God knows what'll happen as the water can't go anywhere.

I've got Evohome in my house so the living room rad has a smart TRV but I have no TRV on my bathroom radiator, so that acts as the bypass in my house, it means it's always on but for the bathroom that's fine.

It's a Tado system. Yes the room stat controls the fire up of the boiler when needed in the living room. Boiler doesn't shut down if other rooms with smart TRV's are still calling for heat.

I didn't realise that one valve had to be left open because I've been closing the manual valve to stop the living room overheating when other rooms are needing heat.

 

[fronty]

It's a Tado system. Yes the room stat controls the fire up of the boiler when needed in the living room. Boiler doesn't shut down if other rooms with smart TRV's are still calling for heat.

I didn't realise that one valve had to be left open because I've been closing the manual valve to stop the living room overheating when other rooms are needing heat.

I only use a bypass rad because I don't have a bypass valve on my system but you might have one somewhere. Do you have a hot water cylinder or have you got a combi boiler? I think on a combi the bypass is internal but if you have a hot water cylinder it will probably be in the airing cupboard somewhere. If you do have a bypass valve then you can probably put a smart TRV on the living room rad, it's mad having to manually shut that off when the room gets too warm.

 

[fronty]

Or take the TRV head off your bathroom rad, make sure the valve is open and use that as your bypass.

 

[MartinW]

I only use a bypass rad because I don't have a bypass valve on my system but you might have one somewhere. Do you have a hot water cylinder or have you got a combi boiler? I think on a combi the bypass is internal but if you have a hot water cylinder it will probably be in the airing cupboard somewhere. If you do have a bypass valve then you can probably put a smart TRV on the living room rad, it's mad having to manually shut that off when the room gets too warm.

Thanks for the info.

My boiler is an Viessmann open vent boiler so I don't think that's a combi? I don't have a hot water cylinder that I know of (no airing cupboard either) but maybe it's in the loft?

However, reading on the Viessmann website it lists one of the 'features' of my boiler is 'No pump over run required'. Is that the same as a bypass?

 

[fronty]

Sounds like you have the same boiler as me, Viessmann Vitodens 100 WB1B (open vent), what a coincidence. It's a traditional style boiler so you should have a hot water cylinder somewhere, maybe it is in the attic. This boiler does not have a bypass built in so you might have one on your system somewhere near the hot water cylinder.

Pump overrun is something separate, mine also has no pump overrun, it basically means the pump will stop running as soon as the boiler shuts down. Viessmann state it's not required but I do feel sometimes it would be nice if I could keep it running for a minute or two just to circulate the remaining latent heat from the heat exchanger, but hey I'm no expert.

Maybe stick your head in the loft and see if you can see a hot water cylinder, they are quite big so you can't really miss it, it's hard to describe what the bypass valve looks like. You could try searching google images to get an idea.

If you have no idea, then just play it safe and take the TRV head off your bathroom rad and fit it to your living room rad.

 

[MartinW]

Sounds like you have the same boiler as me, Viessmann Vitodens 100 WB1B (open vent), what a coincidence. It's a traditional style boiler so you should have a hot water cylinder somewhere, maybe it is in the attic. This boiler does not have a bypass built in so you might have one on your system somewhere near the hot water cylinder.

Pump overrun is something separate, mine also has no pump overrun, it basically means the pump will stop running as soon as the boiler shuts down. Viessmann state it's not required but I do feel sometimes it would be nice if I could keep it running for a minute or two just to circulate the remaining latent heat from the heat exchanger, but hey I'm no expert.

Maybe stick your head in the loft and see if you can see a hot water cylinder, they are quite big so you can't really miss it, it's hard to describe what the bypass valve looks like. You could try searching google images to get an idea.

If you have no idea, then just play it safe and take the TRV head off your bathroom rad and fit it to your living room rad.

Thanks for all your help.

When I get chance I will get up in the loft and take a look but, as you've mentioned, maybe I'll remove the smart TRV from the bathroom, open the valve and have the smart TRV placed on the living room rad instead.

Thanks again.