Why is my boiler overheating?

HotStuff

I'm using Tado radiator thermostats with the Internet Bridge and my existing boiler thermostat. I thought I could leave the boiler on permanently and use the smart schedules to control the rads (Tado technical support agreed this would work). But the boiler has cut out due to overheating twice in two days. I've gone back to my boiler timer for now but does anyone know why this might be happening?

Les_Parry

If you have a situation where the boiler is on but all the Radiator thermostats are closed, then, this would cause the problem you are seeing. It is generally recommended that one radiator does not have a thermostat on it to act as a bypass.

HotStuff

Right thank you. I had assumed that even if it was left ON the boiler would know if it wasn't required and would shut itself off.

Les_Parry

No, something has to turn off the boiler. Usually a room thermostat would, when the required temperature was reached.

In my case I started with the Smart Thermostat and the extension box to control the boiler. Then I added the Radiator Thermostats afterwards. My bathroom radiator does not have a thermostat, so it is the bypass for the system.

samd

Just to add to Les points above, using my setup as an example, when the last device has stopped calling for heat, it takes about 4 to 5 minutes for the boiler to stop circulating the water through the un-TRV'd radiator in order to cool the boiler's innards.

BOLD - new title!

HotStuff

I see. And in your case, does the Smart Thermostat tell the boiler when to switch on/off according to the demand from the Radiator Thermostats?

HotStuff

Oh thanks samd. You answered my question 3 minutes before I asked it 😄