I am considering fitting a thermostat to my central heating system which at present is a combi boiler with TRV,s fitted to all rads.
I am told it is not advisable to have TRV,s fitted to the rads in the room where the thermostat is fitted.
Would it be ok however to either set the TRV,s to max or remove the screw on head to save me having to change the radiator valves?
Any thoughts appreciated.
Marc
Yes, as long as the room stat opens *before* the TRV closes, you'll be ok.
Probably safest to remove the bellows assembly - but just setting it to max may be sufficient.
Roger
How old is your system?
It is possible that an alternative system to a room thermostat is installed. This achieves boiler interlock by detecting flow on an automatic bypass circuit and shutting the boiler down when it is detected. If so, your upgrade will not be appropriate. If such a system is not installed, then the room thermostat is an excellent idea.
Although it could work by turning the TRV on full, it is better to install lockshield type valves at both ends to prevent someone operating the TRV and thus causing inefficiency in the controls.
Christian.
Yes, I've heard of this - but don't understand how it works.
In particular, what starts the boiler up again? Does the pump have to run all the time so that flow through the rads restarts when a TRV opens - stopping the bypass flow and starting the boiler?
Roger
Either the pump runs at a slow speed (but with enough pressure to open the automatic bypass), or the pump could pulse every ten minutes to determine if any TRVs have opened. If there is no bypass flow, the boiler can be allowed to fire.
This has the advantage of acting as an anti-cycling feature. I don't know if anyone produces a unit with the correct logic to do this, but it wouldn't be difficult to do so with a little electronics knowledge.
Christian.
It's starting to get complicated! I think that if I were going for this level of complexity, I would rather have a zone valve on each rad controlled by a room stat in each room - and with the volt-free contacts on the zone valves being connected in parallel to control the boiler and pump when any combination of rooms required heat (described as S-Plan-Plus in
Roger
But then that can get very expensive. Also, it is difficult to site the zone valves so that they are accessible. The easiest way is to have a manifold system with all the zone valves in a cupboard. However, this takes space and the pipe runs have to be installed with this topography in mind.
An alternative is to use motorised radiator valves instead of TRVs. These can be wired up to local room programmable thermostats. This will be cheaper and easy to retrofit to an existing installation. The irony is that without the microswitches of the zone valves to run the boiler off, you'd still need to implement the automatic bypass interlock anyway, to detect when the valves were open. (Although this could be done electrically too, with a load of wiring and some OR logic).
Christian.
As long as each valve has a pair of contacts which close when the valve opens, and which are completely separate from the motor supply, the only OR logic required is to connect all these contacts in parallel - then, whenever or or more valve is open, the boiler and pump will run. You will still need a by-pass circuit - but only to cope with pump over-run while the boiler cools after the last valve has shut. This doesn't need any fancy pressure switches - but a pressure-operated auto by-pass is preferable to a permanently open one.
Roger
Indeed. But motorised radiator valves have no such contacts. They are, however, much smaller and less obtrusive than a full 22mm zone valve.
Christian.
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