Potterton Puma 80e not working

[awksed]

Hi All
I have a potterton puma 80e which is not working after being left idle for 5 weeks. If I turn on a hot water tap, it gushes faster initially than it used to (but then slows down again back to how it used to be) but doesn't manage to cause the boiler to fire up. I am having to turn on the hot water tap, run to the boiler and flick the "Boiler" switch to On and then run back and have my shower and then flicking the "Boiler" switch back to standby after my shower. The central heating function doesn't seem to work at all (either from the control unit or when I flick the "Central Heating" switch on the boiler to "Constant"). The "HW Dem" LED is on all the time. Any suggestions will be greatly appreciated.

 

[Agile]

The hot water demand switch seems to be jammed on.

But in addition you seem to have another fault preventing the boiler from operating in DHW mode.

Obviously you have rather neglected getting your boiler properly serviced and, when required, repaired.

The obvious advice would be to get a competent boiler engineer to diagnose and repair all the issues.

Tony

 

[awksed]

OK, I think I've fathomed this now. The ch will not come on if the boiler switch is in standby. Also, it will not come on if the system thinks there is a hot water demand. The problem appears to be that the microswitch has rusted a bit and so sometimes sticks in the on (closed contact) position. So after the hot water taps are turned off, the switch is stuck on and the boiler is still firing until it trips out through over heating. A bit of oil seems to have temporarily fixed the sticky microswitch (although the real fault might be a leaky hw flow switch which caused it to rust in the first place, but I can't see any leaks). I'll replace it as its only a tenner. But then I had a new dilemma. Sometimes the boiler would fire for no reason whatsoever (no hw demand, no ch demand). On investigation, I found that as you turn off the cold taps, the hw flow switch spindle would move out a little (you can see the spring in the hole getting compressed), not the full amount as if you had turned on the hw taps, but enough to switch on the microswitch and for it to get stuck. So I unsrcewed the microswitch by one turn and everything seems fine now.
My question is this, (if anyone is still awake and reading this) is it normal for the operation of the cold water taps to have a small influence on the hw flow switch?

 

[Agile]

Its not normal but will occur if you have whats called a dead leg.

Thats a length of closed off pipe going nowhere which is full of air and acts like a spring.

Its usually a pipe going towards the loft which has not been removed when a cylinder system was replaced by a combi.

Tony