Potterton Puma Combi Boiler - low pressure light

[scotlanduk]

No you don't need a new boiler!
The Domestic HW flow switch is not hard to deal with.
It's shown here http://www.partsarena.com/baxi/System/DATA/Dx/DS1/installation/2248/I04-2248/I04-2248.htm
See Fig 17 P26 and fig 22 P 32
Do a search - has been mentioned a few times!

Hiya, thanks for the paperwork, can't read the fault finding guide but thanks anyway. We will buy and change the water flow switch and let you know how we get on. What does it mean if a red light is on all the time on the circuit board? This light is on all the time, regardless of what the rest of the boiler is doing - which is nothing most of the time. Any ideas?

 

[kevplumb]

it thinks the hot tap is running cos the flowswitch is telling the boiler theres flow cos its stuck

 

[scotlanduk]

it thinks the hot tap is running cos the flowswitch is telling the boiler theres flow cos its stuck

If that is the case, if we replace the flowswitch this will solve the problem? We changed to circuit board a month ago, so it can't be that - I hope!!!

 

[kevplumb]

disconnect one of the wires on the flow switch and see if the boiler behaves if the red led is on its calling for water

 

[scotlanduk]

disconnect one of the wires on the flow switch and see if the boiler behaves if the red led is on its calling for water

Now, back to basics. We have replaced the circuit board, the pressure relief valve, the hot water flow switch, the micro switch and now we have just changed the diaphragm flow switch. Pressure is on 1.5 bars constantly. Boiler will not fire up at all, pilot light is lit by the way.The boiler sounds okay, you can hear water moving about inside but, if the boiler won't fire up we have cold radiators and when you turn on the hot tap, the red light comes on on the circuit board. What can possibly be sticking now? We have replaced most of the parts now, still nothing happening.

 

[scotlanduk]

Behaviour of the pressure switch isn't making sense.
Disconnect boiler from mains elec.
Undo the obvious screws until you can see the PCB. Bottom left is the connector for the pressure switch, two wires the same colour, yellow I think.
Unplug the connector from the pcb.
The boiler will now ignore the pressure, so it'll light. What does the pressure do? It should be 0.7 - 1 bar cold, a bit more hot. The pressure switch should only come on below about 0.3 bar though that varies.
Don't leave the switch disconnected, because it's there to protect the boiler if the water goes too low.

We unplugged the yellow leads on the PCB - basically nothing happened. Boiler did not fire up at all, red light on the PCB came on when we turned the hot tap on.

 

[kevplumb]

not sure but have a look at the high limit stat if theres a button btween the wires press it

 

[scotlanduk]

not sure but have a look at the high limit stat if theres a button btween the wires press it

Could not find high limit stat - where is it? Also fan has stopped working, so now need to replace this part. Fun eh??

 

[kevplumb]

on the right at the top where the heat exchanger is

 

[ChrisR]

WHile you're in there, take the pcb out and look at its top left corner on the back. Its an even bet that the corner pin has unsoldered itself. If you need one I have some cheap. The fans stick, went to one tonight which just needed a poke! I'll replace that one soon. Again let me know if you need one, they can be expensive.

 

[dapa60]

Behaviour of the pressure switch isn't making sense.
Disconnect boiler from mains elec.
Undo the obvious screws until you can see the PCB. Bottom left is the connector for the pressure switch, two wires the same colour, yellow I think.
Unplug the connector from the pcb.
The boiler will now ignore the pressure, so it'll light. What does the pressure do? It should be 0.7 - 1 bar cold, a bit more hot. The pressure switch should only come on below about 0.3 bar though that varies.
Don't leave the switch disconnected, because it's there to protect the boiler if the water goes too low.

disconneced switch as discribed .boiler worked .reconnected switch heating ok.hot water then would not turn off. suspect stuck diverter valve,has done this before!
have taken out valve and lubricated pin with silicon in the past,hope this will work again. thank for advice dapa60

 

[jimhet]

ChrisR wrote: Behaviour of the pressure switch isn't making sense.
Disconnect boiler from mains elec.
Undo the obvious screws until you can see the PCB. Bottom left is the connector for the pressure switch, two wires the same colour, yellow I think.
Unplug the connector from the pcb.
The boiler will now ignore the pressure, so it'll light. What does the pressure do? It should be 0.7 - 1 bar cold, a bit more hot. The pressure switch should only come on below about 0.3 bar though that varies.
Don't leave the switch disconnected, because it's there to protect the boiler if the water goes too low.

Thanks ChrisR U R A Star. I couldn't find my service manual [ not that it mentions how to bypass a faulty pressure switch] and you're advice was spot on.