Potterton Combi 80 Hot Water but no Central Heating

5 Mar 2009
Reaction score
United Kingdom
After a couple of months of every now and then having to reset the lockout button after having used the hot water tap for showers, baths etc the whole boiler shut down.
Changed the Microswitch and it worked fine for a couple of days until the lockout button started to need resetting every few minutes and the boiler shut down again.
Then changed the Water Flow Switch and now the hot water is fine but no central heating. When I switch on the central heating it fires up after around a minute a lot of hissing ensues culminating in hot steam being released from the Auto Air Vent and the flame going out. Also if I turn on a tap at this time the water is STEAMING hot.
Suspect the Wax Capsule Head or Diverter Valve. worth changing the whole unit including Wax Capsule Head or just the WCH. Could it be something else? The pump seems OK. There is what looks like a small leakage at the top of the WCH - dried green limescale? I'm sure that wasn't there last week. The pressure gauge also keeps on dropping to 0.
Just ran this for a few minutes, Wall thermostat turned on, central heating turned on at boiler, radiators on 5 and hot water tap running.
Boiler fired up and flame on constant.
Hot water tap at normal hot temparature
Pressure gauge at a constant 1 bar
Radiators stone cold
Turned of hot water tap,
Clunking noise from boiler
Pressure gauge up to 2 bar
Flame went out
Steam being emitted from Auto Air Vent
Lockout light came on

Thanks if you can help.
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Check pump again....just for starters....unsrcew the center plastic nut...pull out and check rotates freely then power up and check it rotates.

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