Potterton Puma Combi Boiler - low pressure light

[scotlanduk]

Please help, no heating or hot water for two weeks!! The low pressure light keeps turning on, so boiler switches off. We have changed the leaking pressure relief valve, also both the hot water flow switch and micro switch. Still no heat or water. When you raise the pressure in the boiler - ie adding more water - the low pressure light kicks in again and off goes the boiler. If the pressure drops to the minimum, the low pressure light goes off for a short time before coming on again. Any ideas?

 

[ChrisR]

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.

 

[kevplumb]

eeeeehhhhh you cant advise somebody to disconnect a safety feature

non of us would dream of doing such a thing

 

[PEDANTICVINDICTIVEMAN]

Mmmmmmpppfffffffffffff

 

[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.

Thanks for the swift reply, did as requested, the boiler fired up and was fine after we plugged the connector in again. The pressure stayed at 1.5. Then I turned on the hot water tap in the sink!!! Pressure went straight up into the red - past 3 - and the flame went out on the boiler amid lots of loud noises. The only good thing was the low pressure light did not come on. We also cant turn the boiler off once it is on. Anymore ideas?? We have reconnected the switch by the way.

 

[kevplumb]

expansion vessell needs pumping up
try a search
was going to say repressureisaton but cant spell it

 

[ChrisR]

Still something odd. Usual culprit if the boiler won't go off is the tap water flow detection switch. That puts a RED led on on the pcb when the tap's open. SOmetimes they stick and the boiler stays on. See if yours is stuck on. If so the CH would get hotter and hotter until it overheated and the boiler cut out, but that would takea while.
I cant immediately think what's wrong for the thing to overheat when the tap's turned on. Anyone?

Unless the pump's dead as well. Do the rads get warm?

 

[kevplumb]

is the red led on the pcb alight when the boiler wont switch off
(note to self read the last reply before jumping in

 

[scotlanduk]

Still something odd. Usual culprit if the boiler won't go off is the tap water flow detection switch. That puts a RED led on on the pcb when the tap's open. SOmetimes they stick and the boiler stays on. See if yours is stuck on. If so the CH would get hotter and hotter until it overheated and the boiler cut out, but that would takea while.
I cant immediately think what's wrong for the thing to overheat when the tap's turned on. Anyone?

Unless the pump's dead as well. Do the rads get warm?

Hello again, the radiators do get hot, but we can't have heat and water at the same time. When you turn on the tap for the water all is well until you turn off the tap. Then we get a terrible noise from the boiler and steam shoots out of the release valve at the top of the boiler. then the flame goes out and we have to relight it again. Where is the tap water flow detection switch? We have noticed that a red light stays on on the circuit board even though the boiler shouldn't be on, ie hot tap isn't running and heating is off - boiler still fires up. Do you think we need a new boiler??

 

[scotlanduk]

is the red led on the pcb alight when the boiler wont switch off
(note to self read the last reply before jumping in

Incase you didn't read my reply to Chris, yes the light on the circuit board does stay on when boiler won't switch off. I think we need a new boiler unfortunately. Giving up hope after three weeks without heat or hot water, plus electricity costing us a fortune due to boiling kettles constantly.

 

[ChrisR]

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!

 

[kevplumb]

 

[ChrisR]

You're up late, mate!

 

[kevplumb]

im up early marra

 

[Softus]

That partsarena URL came in handy then!