DIY Doctor

Changing 3 Radiators With Lockshield Valves to TRV Valves

Postby ApolloFly » Wed Sep 25, 2019 2:01 pm

Hi. Hope someone can help please.
I have just been reading through the article on this site about changing TRVs

I have 17 rads in my house and have been looking at the new Hive smartphone controlled valves. However I still have 3 "control" valved rads that dont have TRVs.

I am pretty sure that this para in the article is what I mean.....

Building Regulations state that all new and modified wet central heating systems must have a TRV fitted to every radiator (apart from one where the room thermostat or programmable thermostat is installed, typically in the hall)

However since we had Hive installed, the room where the rads without TRV's are, don't of course have a heating thermostat control, as the hive thermostat control was put in another location.

So, my question is this - can the 3 rads with lockshield valves (I think they are called) be changed to TRVs, so the whole house has them?

Thank you. Hope I've explained it all OK.
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Postby ericmark » Wed Sep 25, 2019 8:47 pm

One the building regulations are very vague and don't actually state what can and can't be done as such, but the approved documents explaining the regulations do, but they are not the regulations.

As to TRV's they can clearly all turn off, when this happens the by pass valve will open returning hot water to boiler which will in turn turn the boiler down or off, so to have all TRV control there must be a by-pass valve or some where for the water to flow, for example thermo syphon domestic hot water heating or non TRV controlled radiators often the bathroom towel rail.

But if there is a by pass valve, some times external and some times inside the boiler then all radiators can have TRV's fitted.

I use Energenie TRV heads and they work very well, but reading the write up on Hive there system is better, you can turn the wall thermostat down low and the TRV heads send a heat on demand signal so heating stays running until all heads stop asking for heat.

From the adverts it seems the wall thermostat runs the boiler for 30 minutes after each request, so as long as kept lower than the TRV heads then unlikely to be a problem. But can't say 100% no problem.

This house had the bathroom radiator and domestic hot water on thermo syphon with no control other than time, and rest all TRV controlled, this means no problem for boiler, but the pump could cavitate, with the three main rooms and wall thermostat being linked this is unlikely, but still possible, however cost of pump not really worried. The boiler will not have a problem.

Most of the TRV heads are just blue tooth, some still wax, and 4 are wifi linked to Nest thermostat, as to how well it works I don't know not done a winter yet.
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