Post by decker
I have a strange issue with my central heating. Moved into a new house
3 years ago and heating worked fine for a year, then last winter we
had an issue where it wouldn't turn off.
Post by decker
Has anyone seen this issue before and have any suggestions to fix,
other than just replacing the boiler?
I take it that the plumber has tried removing one wire from the hall
thermostat? If not, try it. Leave it off until you are sure that the
boiler is not being told to fire because the 'stat is faulty. If you leave
it disconnected, it will not call for heating at all. Once you have tried
this, you'll know that the 'stat is not the problem. One down, not many to
Disconnect one wire from the timer / controller, preferably the wire that
feeds to the boiler live mains input. Leave it disconnected to make sure it
is not the controller that has gone faulty and is still calling for heat,
even when you think it is off. Two down, less bits to go.
Make sure that the controller is actually connected properly. The hall
thermostat and the zone valve should be connected in a loop, so that when
the 'stat opens, the valve has to close to tell the boiler to stop firing
up. This is also true with any water storage heating appliance with a
thermostat on it. Make sure they are connected in a loop wiring scheme with
the zone valve, so the zone is the only thing telling the boiler what to do,
and when to do it.
The wiring system should be connected in the following way.
Timer / Controller with live feed and neutral to make it work.
Switching in the controller for the heating system should be connected
through the hall thermostat, then on to the central heating connection of
the zone valve. From the valve it should be connected to the boiler to call
Hot water switching in the controller should be connected through the
thermostat on the hot water cylinder, then on to the hot water side of the
zone valve. The valve switching is then connected to the boiler to call for
This simple connection scheme makes it easier to diagnose faults with the
whole system. If the zone valve occurs a fault on the central heating
switching, the heating won't come on. Respectively, if the valve has a
fault on the hot water switching, the hot water don't work. If the hall
'stat has fault, the central heating will either stay on continually,
because the thermostat has stuck closed, or it won't come on at all because
the 'stat has stuck open. Again, this same fault occurrence on the hot
water 'stat shows the problem in the same way.
It sounds like you have a stuck thermostat or that two 'stats are fighting
with each other for the call to fire the boiler. When you say you have to
switch the whole lot off, it occurs to me that an automatic device on the
boiler is sticking in the closed (call) position until the power off cycle
resets it. So it is something that needs power on, to hold it closed
(calling for heat).
In this case, you have something that needs powered down to make it reset,
which could be the zone valve because it is wrongly connected into the
system. Or the controller switching is sticking closed (calling for heat)
because it is connected incorrectly or is being forced into fault condition
by some other wrongly connection scheme. It is simple to follow the
connections from either side of the controller. Look at where the wiring
goes from the controller to each of the devices, writing down how each
device is connected into the whole system. Check it against the wiring
scheme I have given above to make sure.
Remember that the electrician (whatever) will have used both, or maybe all
the cores in the cables to make his loop wiring. So following a brown wire
from the controller to the hall thermostat, will return from the hall 'stat
as a blue wire (assuming those colours have been used). But you get the
Good luck with your fault finding.