"Can't have TRV on all rads" query..

Kiteview

When we moved into our home we installed (non-smart) TRVs on all our radiators bar one. At the time, the plumbers claimed that one radiator in the system had to be left without a TRV on it for some reason. Does anyone know what the reasoning behind that claim was or is?

I ask because we have now upgraded to Smart TRVs as part of a Tado upgrade and I can't understand why I shouldn't put a smart TRV on the radiator that previously didn't have one.

PS I should add that there is one two-way valve in our heating system. Previously that valve could shut off the entire radiator circuit via a (non-smart) room thermostat once the set temperature was reached (and the boiler would then just heat the hot water). Now, after the Tado rewiring, that two-way valve gets shut off when all the radiators with Smart TRVs reach their required temperature and switch off their CH signal (ie "call" for the heating to be on).

astrofool

When not using smart TRV's you would need at least one rad where the heat could be "dumped" as the operation of the TRV is independent of the boiler on/off (so if you had it timed to come on at 6PM and all TRV were at temp, the hot water would just continually circle the system, I don't think this should cause any harm unless there was pressure issues).

With the smart TRV, they are the signal to the boiler to fire, so it should be fine for each rad to have a smart TRV (the rad is asking for heat vs. a thermometer disconnected from the rad).

Lenar3556

https://www.boards.ie/discussion/comment/122745514#Comment_122745514

Yes, but there may be no route for the water to circle the system at all as all radiators could potentially be closed.
In such a circumstance, the pump would be pumping against a dead head.

But as you say, the new system should solve all of that.

Kiteview

Thanks for the responses.

Just to clarify one point, as there is a two-way valve that shuts off the flow from the boiler to the radiators when the smart TRVs no longer need it, I presume that any heat that would need to be “dumped” would currently just go to the hot water circuit, right?

Also, should we decide at a future date to put in an additional two-way valve to control flow to the hot water circuit, then would we need to add some sort of automatic by-pass valve as a safety precaution in case both valves are shut off at the same time? Or is that sort of valve there as standard in most domestic systems? If so, where would it typically be? Near the boiler?

Lenar3556

https://www.boards.ie/discussion/comment/122746611#Comment_122746611

Domestic heating systems don’t typically require a heat leak or ‘dump’. There is generally sufficient such capacity within the boiler itself and is this is considered in the design of the boiler thermostat. What can need to be considered is avoiding a scenario whereby a circulation pump is running, and no path to pump to, and this is why your plumber wished to have one radiator without a TRV in the past.

An automatic bypass is a simple device which can solve the above if it was an issue, likewise can act as a heat leak if for any reason that was an issue. But I don’t think you need be particularly concerned about either given your plans.