FOR INFORMATION - PROBLEM SOLVED
My suprima was constantly firing up for a couple of minutes, turning off temporarily and then firing up again - on the hottest day of the year so far, when thermostat not demanding heat and timer control switched off. 2 two port valves fitted. Result was very hot water circulating the radiators constantly.
Suggestions on this forum and elsewhere included:
faulty thermistor
sticking valve
Thinking about this overnight, I was sure the problem was going to be related to the valve as there would be no reason for the thermistor to even be operational if the other controls were switched off and would not result in any water circulation.
On checking the valve, taking the valve control unit off, I found it to be normal. No sticking or difficulty opening/closing with my fingers.
However, the control unit lever was stuck down on the switch. Wiggling the synchronous electric motor resulted in the mechanism releasing from the switch and the heating fully shutting down. The motor was noisy and on testing continued to fail to release when the heating system (thermostat or timer) demanded it.
I replaced the synchronous electric motor - an easy and cheap job - and all is now well. The replacement motor is silent.
At the same time, I checked the operation of my other valve control unit, the one that would control the hot water if I had it fitted to the valve. I don't as I keep the HW valve open all the time the CH is on over winter so the water tank is constantly kept heated, due to the demands in my home. I let this unit dangle in the airing cupboard.
I discovered the toothed mechanism was slipping part way through the movement towards the switch, meaning the switch would never be operated and hence the valve would never be opened. The problem was the teeth on the synchronous electric motor had worn and whilst the teeth on the lever mechanism seemed in good condition, this group of parts were loose and the wobbling around against each other seemed to make the synchronous electric motor teeth jump out, so the spring loading took the arm back to its start position, only to repeat the process again.
I replaced both the synchronous electric motor and the lever mechanism and all appears to be well again.
My suprima was constantly firing up for a couple of minutes, turning off temporarily and then firing up again - on the hottest day of the year so far, when thermostat not demanding heat and timer control switched off. 2 two port valves fitted. Result was very hot water circulating the radiators constantly.
Suggestions on this forum and elsewhere included:
faulty thermistor
sticking valve
Thinking about this overnight, I was sure the problem was going to be related to the valve as there would be no reason for the thermistor to even be operational if the other controls were switched off and would not result in any water circulation.
On checking the valve, taking the valve control unit off, I found it to be normal. No sticking or difficulty opening/closing with my fingers.
However, the control unit lever was stuck down on the switch. Wiggling the synchronous electric motor resulted in the mechanism releasing from the switch and the heating fully shutting down. The motor was noisy and on testing continued to fail to release when the heating system (thermostat or timer) demanded it.
I replaced the synchronous electric motor - an easy and cheap job - and all is now well. The replacement motor is silent.
At the same time, I checked the operation of my other valve control unit, the one that would control the hot water if I had it fitted to the valve. I don't as I keep the HW valve open all the time the CH is on over winter so the water tank is constantly kept heated, due to the demands in my home. I let this unit dangle in the airing cupboard.
I discovered the toothed mechanism was slipping part way through the movement towards the switch, meaning the switch would never be operated and hence the valve would never be opened. The problem was the teeth on the synchronous electric motor had worn and whilst the teeth on the lever mechanism seemed in good condition, this group of parts were loose and the wobbling around against each other seemed to make the synchronous electric motor teeth jump out, so the spring loading took the arm back to its start position, only to repeat the process again.
I replaced both the synchronous electric motor and the lever mechanism and all appears to be well again.
