Old boilers and TRV's

[ericmark]

Looking to move house, many have old boilers fitted, and I will want to in fullness of time upgrade, but the boiler will be changed by some one registered as gas safe, but rest done by myself, so would prefer to fit TRV's and new lock shield valves before the boiler so all ready for new boiler.

However not sure what will happen if I fit TRV's to old boiler? Last house TRV's fitted upstairs but not on ground floor and the Myson fan assisted radiator has no lock shield valve so always a flow, some boilers have a by-pass inside boiler, some need it exterior, so not keen on fitting a by-pass valve which may then need removing once boiler changed.

Also not sure how TRV's will work with a non modulating boiler? I know how they work with modulating boiler, but if the boiler is not running I would assume the valve will open more and more until fully open, then when boiler runs radiator will heat up completely before valves can close again, this of course still happens with a modulating boiler when turned off over night, but on switch on house is cold so there is time for valves to shut. But with a wall thermostat one would expect boiler to run at least once an hour, so will fitting TRV's end up increasing the hysteresis.

So should they be left wide open until new boiler fitted, i.e. don't fit heads, and what about the kitchen, if I fit a Myson kick space in kitchen, will this work OK once boiler changed. Or will the fan stopping cause the modulating boiler to throttle back, even when other rooms not to temperature, can I actually fit a TRV to a Myson? I know fan will not kick in until warm enough.

Just trying to work out order of events once I move, would be good to drain system and fit all TRV's and new lock shield valves before we move in so no furniture in the way, but likely I will not be able to wait for a boiler to be changed before moving in.

 

[ianmcd]

just fit the TRVs no need to leave them fully open set them at what you want and just leave one rad without a TRV Usually the bathroom rad or towek rail and the boiler will know when everything is up to temp and just in case your boiler needs a by pass you have created one and you can address the by pass rad when fitting your new boiler, note this wont work with an S plan system, you would need an external by pass before the valves

 

[ScottishGasMan]

Modulation of a boiler doesn't really have any effect on TRVs.

Essentially, TRVs have a capsule in them, as the air temp in the room raises the capsule expands and closes the water flow to the radiator. The boiler (assuming it has no modualtion) will just cut in and out depending on teh temperature of the water leaving it, so if some TRVs have closed down then the boiler will simply be fired up for less time (still saving gas and keeping rooms more comfortable) Even a modualting boiler will still run to full temperature before shutting the burner off.

A kick space heater has a constant flow through it, so when fan is off then hot water will be returning to boiler, which will cause an old non modulating boiler to cut off quicker and possibly cycle more, it will cause a modulating boiler to modulate down more if there is warmer water returning to it. However most kickspace heaters you can just leave fan turned on (the fan will only run when the kickspace has warm water in it so when heating is off and flow cools fan will go off)

Never seen a TRV/Thermostatic valve for a kickspace, although depending on your pipe layout and budget you could fit a pair of electronic zone valves so there is no flow through the kickspace when its not in use.

All in, go ahead and get the TRVs fitted, will do no harm to an old boiler (a little more cycling) And new boiler will work fine with them to. As said leave one or two radiators without them for a constant flow if the old boiler doesnt have a bypass (must be a method of keeping water flowing round boiler in event that all TRVs have closed off at same time)