potterton combi 80 noisey boiler

paulfaulty · 30 Jul 2005

Can anyone out their help me ? My boiler makes a really loud rushing steam boiling sound after I run the hot tap and turn it off. It trips off then and I must press the reset. both heating and water work fine.

ChrisR · 30 Jul 2005

Sounds like it's boiling?

Could be air trapped in it. There's an automatic air vent top left, cap of which should be undone a couple of turns.

Could be other odd things like a slow pump. Does it do it when the heating has been on for a minute or so then switches OFF?

All sorts it sort of could be!

bradleybear · 31 Jul 2005

DHW Flow switch sticking, rushing noise is wax capsule in diverter valve being forced open due to immense latent heat in boiler, thus trying to force heat away from your boiler around the rads. Can be cleaned or ultimately replaced, part costs about £6.

ChrisR · 31 Jul 2005

Can you explain better BB?
The Domestic hot water flow switch is not connected to the wax capsule or diverter valve body. There can be no force to push the diverter/wax capsule cos the other end of the waterway is open.
Pumas boil if the DHW flow switch sticks after quite some time- when the rads circuit overheats. Not as soon as theHW is turned off. (The boiler would stay ON after the HW is turned off)
The DV could be stuck/not working properly due to waxstat or otherwise - how good is the HW output Paul?
I can't think of anything much on a combi80 which costs only £6!!

gazthepottertonengineer · 31 Jul 2005

best way to test it is to see if the red light goes out on the pcb after you turn hot tap off if it doesnt then replace the microswitch

if it still does it then you need new hot water pressure sensor which is what the microswitch screws into

bradleybear · 31 Jul 2005

Chris R

If the DHW is sticking on after the tap has been turned off (easily checked by the red light on the PCB), the burner stays on. Now being a dual pass heat exchanger, contained within the waterways, is domestic and central heating water. Logically, if the burner stays on, both waters are heated. Now we know the tap hot water tap is turned off, so no cold water is passing over the wax capsule in the diverter valve, therefore, the red hot central heating water will try and force the diverter valve open. As soon as that wax capsule gets red hot, the diverter valve will partially open. This is where we get the rushing noise. The central heating water is being pushed through the partially open diverter valve. The diverter valve is purely thermo mechanically operated, so as soon as hot water hits the diverter valve, it will try and open.

As for the part costing £6, thats how much the microswitch normally costs, as that is the most common failure on these boilers. The flow switch assembly it screws into can fail, but it is more common for the switch to stick due to being dirty/stiff.

paulfaulty · 3 Aug 2005

ChrisR said:
Sounds like it's boiling?

Could be air trapped in it. There's an automatic air vent top left, cap of which should be undone a couple of turns.

Could be other odd things like a slow pump. Does it do it when the heating has been on for a minute or so then switches OFF?

All sorts it sort of could be!

paulfaulty · 3 Aug 2005

bradleybear said:
Chris R

If the DHW is sticking on after the tap has been turned off (easily checked by the red light on the PCB), the burner stays on. Now being a dual pass heat exchanger, contained within the waterways, is domestic and central heating water. Logically, if the burner stays on, both waters are heated. Now we know the tap hot water tap is turned off, so no cold water is passing over the wax capsule in the diverter valve, therefore, the red hot central heating water will try and force the diverter valve open. As soon as that wax capsule gets red hot, the diverter valve will partially open. This is where we get the rushing noise. The central heating water is being pushed through the partially open diverter valve. The diverter valve is purely thermo mechanically operated, so as soon as hot water hits the diverter valve, it will try and open.

As for the part costing £6, thats how much the microswitch normally costs, as that is the most common failure on these boilers. The flow switch assembly it screws into can fail, but it is more common for the switch to stick due to being dirty/stiff.

paulfaulty · 3 Aug 2005

gazthepottertonengineer said:
best way to test it is to see if the red light goes out on the pcb after you turn hot tap off if it doesnt then replace the microswitch
if it still does it then you need new hot water pressure sensor which is what the microswitch screws into

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potterton combi 80 noisey boiler

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