Y-plan central heating system. Out of interest, what happens when all TRVs are off, hot water is off but Room stat is calling

[tpot5]

I am thinking of relying entirely on my Thermostatic Radiator Valves and not the room thermostat.

In order to do this I would need to bypass the room thermostat (or just turn it up high).

So what happens when all TRVs have hit their temperature and switched off and the hot water isn't calling but the room thermostat is up high?

If I understand my heating system correctly, the pump will be running and the boiler will be heating but there will be nowhere for the hot water to go.

Have I understood this correctly?
What will happen in this case?
How can I change the system so that I can rely just on the TRVs?

Do you not have one rad without a trv? If not do you have a bypass valve? I believe this allows water to circulate round the boiler without going out to rads

You need one rad with no trv otherwise the boiler will start 'kettling'; overheating and sounding like it is ready to blow!
I speak from experience

The system should have a bypass valve fitted that opens to allow the water to circulate

@MarieG10 @Ridingthegravytrain

If I get a bypass valve installed would it be practical to switch the pump and boiler off when the bypass valve opens?

I could do this by replacing the room stat with a contact thermostat and placing it on the valve or by using a more direct means of detecting that the valve is open?

I can see that I would need a built in delay or temperature Hysteresis to prevent the system from oscillating

@tpot5 sorry I'm not a plumber. Perhaps you need to ask one

That all sounds a bit more complicated than needs to be. Bypassing the room thermostat removes the boiler interlock and the boiler will continue to cycle even if only a couple of trvs are calling for heat & equally if a couple of trvs are not closing off properly. The bypass starts to open when pressure builds as trvs start to shut down causing a rise in pressure on it. This means water could be passing through it long before all trvs have closed.

If all radiators are sized correctly the rooms should heat up equally, so to remove the trv head in the room in which the thermostat is sited should do the trick. That one radiator then dictates when the system shuts off.