Potterton Puma 100E - having problems

[badminton1000]

Hello, any advice on this problem would be greatly appreciated.

The boiler (when mains is on, boiler switch on, ch switch set to off) fires up instantly and pushes heat out to the radiators. The ch flow pipe heats up rapidly and the boiler (usually, but not always) goes to 'lock-out' and discharges. The fan is working. The CH control / timer unit is working. End result is we're now opertaing the boiler for short periods only, when we need HW, leaving the boiler off at the mains at all (other) times.

Is this a PCB logic problem (obviously I don't want to change the PCB if not necessary) or a mechanical failure (switch, stats) etc.

The red led on the main PCB seems to be lit at all times.

Am competent at part replacement on the boiler, having done so on several occasions, using the fault finding flow diagram in the Installation and Service Instructions, but as the boiler fires up on power on, I'm not able to sequence through the flow chart with any success.

Thanks in advance for any advice.

 

[Gasguru]

Start by checking the hot water flowswitch assembly isn't jammed on or the microswitch siezed/closed circuit.

 

[werewolf]

it will be dhw flow switch.This fault condition is in mi.

 

[badminton1000]

Start by checking the hot water flowswitch assembly isn't jammed on or the microswitch siezed/closed circuit.

The DHW switch appears to be OK, at least I can see the spring moving.
The microswitch looks a bit 'black', so I'll change that first and see if that's the cure. If I put a meter on the terminals of the microswitch, what should I be reading ?

Thanks for the advice.

 

[badminton1000]

it will be dhw flow switch.This fault condition is in mi.

Pardon my ignorance, but what do you mean by "this fault condition is in mi".

Cheers

 

[Gasguru]

mi - manufacturers instructions.

Just 'cos the spring moves doesn't mean its working.

A common fault on this pile of junk is the pin from the round brass lump sticks so although the spring moves, the microswitch is not fully released.

You could just unhook one of the wires from the switch and see if the boiler still fires up with no demand.

Unscrew the microswitch (note how far its screwed in - correct setting in manual) and check this hasn't jammed - they often get waterlogged. Also check its open circuit at rest.

 

[badminton1000]

Big thumbs up to Gasguru and Werewolf !!

Problem solved - replaced microswitch (old one was corroded and stuck) and all now functional. Everyone is happy in the household tonight.

Best Wishes All !