Stanley Gas Fired 80k Twin System cooker

[oilhead]

The installation manual you have gives you all the information you need. Without following the wiring diagram with a multimeter, it is impossible to diagnose the problem. The programmer you have fitted is not the original, but a version of the same unit that performs the same, but is not rated for the temperature it is operating in. Consequently they fail prematurely, yours may have. Which programmable room thermostat do you have? This may have been installed incorrectly.
You should be running with the Stanley in HW and CH mode, with the CH slider in the constant position but if the thermostat has been installed incorrectly, you may have a constant feed to the CH valve. Probably a job for an experienced controls technician.

 

[andytw]

As an owner of a similar vintage Stanley 100k can I beg to differ. I would say that is the original programmer as it says Stanley on it and has Cooker printed on it where a normal 'off the shelf' programmer would say Hot Water. It is of the type that was fitted to our Stanley. They certainly do fail, particularly the slide switches. I had a lot of problems and replaced mine with a Honeywell ST9400C and put it at eye level on the wall near the cooker which is more convenient than having to open the cooker door and reach down.
With a mechanical rather than programmable room stat we have always operated our Stanley as 'Timed' rather than 'Constant' in an 'S' plan system. Did the OP say he had a programmable thermostat, apologies if I missed it.
I would help with a copy of a manual but ours is oil and not gas.

 

[oilhead]

Oops! I only looked at the felt tip writing on it.
Seeing that however, makes me wonder whether the problem is confined to the room stat which OP suggests is programmable. If the installer has taken a direct live feed to it instead of across the normal thermostat connections, then this may override the valve when not required. Twin burner cookers, oil or gas, often pose problems to technicians who only work on boilers and do not follow the wiring diagrams because 'they know it all'. As an example, fitting a frost stat to a Rayburn, rather than bridging the heating circuit, you feed into the Hot Water Off terminal on the junction block.

 

[andytw]

Oops! I only looked at the felt tip writing on it.
Seeing that however, makes me wonder whether the problem is confined to the room stat which OP suggests is programmable. If the installer has taken a direct live feed to it instead of across the normal thermostat connections, then this may override the valve when not required. Twin burner cookers, oil or gas, often pose problems to technicians who only work on boilers and do not follow the wiring diagrams because 'they know it all'. As an example, fitting a frost stat to a Rayburn, rather than bridging the heating circuit, you feed into the Hot Water Off terminal on the junction block.

I can see this will be difficult to resolve. My installation is totally my own, except for the oil side, so I know how it is wired and what goes where. I don't understand what was done here to require the crossing out and writing on the programmer face.

 

[oilhead]

. I don't understand what was done here to require the crossing out and writing on the programmer face.[/QUOTE]
This is what makes me think the room stat wiring is causing the trouble.