Potterton Promax 24 He Plus constantly on

[readerea]

I have a problem that seems to be to do with the connection between the timer and the boiler that results in the boiler not being turned off whenever a time slot expires or the thermostat operates. It bears a strong similarity to the following
http://www.ukplumbersforums.co.uk/c...n-promax-he-plus-fires-up-when-timer-off.html
The boiler is of a similar age but it is a permanent state not spasmodic.
I first noticed what appeared to be something wrong a couple of days ago in that, with the heating off, the hot water cycle would cause the radiators to be warm. When the cycle expired the radiators would cool down. So some sort of inter-connection between hot water and radiators.
Tonight was the first time, due to the good weather, for a week or so that we've had the heating on. I noticed after the timer should have gone off that the boiler was still going even though the timer was off (both the hot water and heating lights on the timer were off).
Nothing I do with the timer can stop the boiler so I had to drop power to the boiler.
It sounds like some sort of valve actuator problem, either mechanical or electrical. The 'leakage' from hot water to central heating, as described above, seems too strong a coincidence. But that would seem to imply some sort of interlock between valve and gas burner.
Any opinions gratefully accepted.
Eddie Reader

 

[jhon lennon]

its your timer mate bet ya

 

[Billy Bob Bob]

its your timer mate bet ya

bet ya its not

 

[mcniven]

lolol

 

[Mike Jackson]

My first port of call would be zone valves but without being in front of the installation with a multimeter you can guess all day.

 

[readerea]

Thanks for all the replies. What are your opinions on the following?
By pure coincidence the house burglar alarm system 'responds' to local electrical surges. for example the flourescent tube in the kitchen being turned on. I can 'hear' the timer communicate with the boiler. I do not have a very good schematic of the boiler, but can see a PCB. My suspicion is that a control signal is sent to the PCB but it is in a locked on state. That is, irrspective of any control signals, it activates all the actuators.
How robust are these PCBs?
Thanks
Eddie Reader

 

[Millsy 82]

You would be better off getting a GSR to look at it we can only give a certain amount of advice. Non of the above advice has pointed to the PCB if you are unsure what you are doing it could end up very costly and still not working correctly.