In an earlier contribution to this discussion,
wrote:

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

You have an S-Plan system - for which a schematic and wiring diagram can be
found at http://content.honeywell.com/uk/homes/systems.htm

With 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.
--
Cheers,
Roger
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