central heating boiler runs all the time

[fisher2312]

I have a profile 50e boiler,it uses an external time clock also made by potterton and there is a romm and tank stat as well as 2 honeywell

2port vavles

Even with the programmer and room stat removed the boiler still runs and the rads get hot, the only way of shutting down the boiler is by adj the boiler stat to low or switching it off.

I am thinking that there is eithera fault on the 2 port valve or there is a fault with the boiler.

can anyone help please.

simon

[The Natural Philosopher]

Stuck switch/ 2port valve.

Replace the valve head.

[Roger Mills]

You have an S-Plan system - for which a schematic and wiring diagram can be found at

such a system, the programmer and thermostats cause the motorised valves to open. When one or more valves are open, secondary switches in the valve actuator cause the boiler and pump to run.

If a valve sticks open - or if the contacts of its secondary switch get welded together - the heating will run, even if there is no demand from the programmer or thermostat.

This is undoubtedly your problem. It *could* be a faulty actuator, but I'd put my money on the 'wet' part of the valve being partially seized so as to be too stiff for the actuator's spring return to close it. If you remove the actuator from the valve and it (the actuator) immediately moves to the valve closed position, this proves it. If this is the case, you may be able to free up the valve by rotating its spindle backwards and forwards. Failing that, it will have to be replaced - which will involve a partial drain-down of the system.

[John]

Is it possible that some terminals have been bridged (for testing / commissioning) and these links have not been removed when connecting the timer and thermostat?