"decker" wrote in message
...
On 4 Dec, 13:56, Roger wrote:
The message

from decker contains these words:

We have a standard Gravity Fed System Setup
Potterton Profile (in garage)
Electronic Timer (in kitchen)
Thermostat (in Hall)
Zone Valve which switches between water and Heating (in airing
cupboard by water tank).

Stuart

Couple of stray points.

You don't mention it but I presume you do have a thermostat on the hot
water tank.

What is the electronic timer? That might have some bearing on the
situation (but on the other hand might not).

--
Roger Chapman

Roger,
The Programmer is a HorstMann (Channel Plus).
Yes there is a thermostat on the water tank, and oddly I checked the
temperature of the water coming out of the taps as it seemed
excessively hot (as the heating had been on for a while).
The water thermostat is set to about 54 but the temp of the water was
about 60 degrees so it appears it is not working.

I agree that if the thermostat was faulty then the Controller would
also need to be faulty as i'd expect both thermostats to be
deactivated if the controller was off but that is not whats happening.

Stuart

If the system is wired from the controller to the thermostat and zone valve
in a parallel configuration, the hot water cylinder 'stat will keep calling
for the boiler to fire. This is wrong, and could be causing the problem you
are experiencing.

The wiring needs to be from the controller, through the hot water cylinder
'stat, through the zone valve and on to the boiler. That way, the boiler
only fires when both the hot water thermostat and zone valve have activated
correctly. If either zone valve or hot water 'stat show fault condition,
the boiler is not signalled to fire.

The same wiring configuration should be used for the central heating side of
the system. From controller to the hall thermostat, through the zone valve
and on to the boiler. The same effect is shown by not calling for heat at
the boiler, if either the hall 'stat or the central heating side of the zone
valve show fault condition.

It still sounds like a wiring fault, or that one of the switching points on
the thermostats of zone valve. You now seem to have found that the hot
water thermostat could be continually calling for hot water from the boiler.
But, are the zone valve and hot water 'stat being activated directly by the
controller, together or individually?