Potterton Suprima 60HE Flow Thermistor problem?

28 Jan 2006
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United Kingdom
Drained water from central heating. Put Sentinel x400 (cold spots in radiators - not air) into FE tank and filled up the system. Switched on boiler. Lockout light - red, Burner light -flashing, Mains light - on. Radiators not heating. Pump very hot to touch. Info on boiler flap says that the sequence of lights means there is a 'Flow Thermistor' problem. I'm assuming that something has happened to the boiler by me draining the water out of the system? Can the Flow Thermistor be fixed by a non-plumber or am I best getting in a central heating Engineer?
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I would suggest there is no problem with the boiler, sounds to me like no water in the pump - turn it off before it burns out.
The reason for no water might be a blocked cold feed.
Thanks Mick. I'd switched off the the system and made sure it's not timed to come on again until problem fixed. Good to hear it isn't likely to be the boiler. Sorry to ask a daft question but I take it that in order to check that the cold feed is blocked or not, I'd need to disconnect the cold feed pipe at the connection point with the pump. I'm assuming I'd need to close the valve on the cold feed pipe to stop a cascade of water coming out. If water (amount between valve and pump) comes out of the pipe then I assume that the cold feed is not blocked?
before doing that try moving any motorised valves into manual open position, vent any airvents in airing cupboard and re vent rads. try venting pump at bleed screw. hopefully you'll be getting water at all of these eventually. if the water doesn't come and you can't hear air hissing out of the bleed nipples etc then yes it sounds like it could be a blocked cold feed, or its airlocked or your ballvalve isn't opening.
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Did as you suggested. Rads vents and hot water cyclinder all giving out water and no air. The pump valve when opened only gave out a meagre amount of water (a drop formed on the valve). When the valve was open I switched on the boiler to see what would happen. Funnily enough the boiler fired up Ok. I switched it off and closed the valve on the pump. Switched on the boiler again but back to the red light (lockout) and flashing light (burner). Ballcock is working OK. I retried switching on the boiler with the pump valve open but it didn't work this time. Any ideas?
by "pump valve" I assume you mean the large screw in centre, not on of the brass valves with "taps" on. With this screw out check if the pump motor turns (I think you have to turn the boiler on to get pump to work)
just to reassure you about the thermistor warnign light. the boiler compares the temperatures measured at the flow and return thermistors to ensure flow rather than using a flow switch. as I think you've guessed the thrmistor itself is unlikely to be the fault
Took out the large screw in the front of the pump a slow trickle of water started to come out, initially with some black iron oxide particles (only a few particles). I switched on the central heating system. The pump made a noise and the pipe to the radiators upstairs was vibrating, assuming with the movement of water. The water coming out of the pump maintained its slow trickle. Switched off after 10 seconds. Tried to bleed the rads again but steady flow of water coming out of them. With my description of what the pump is doing does seem like it is working normally? Any further guidance would be welcome.

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