I have an open vented CH system heated by a potterton suprima 40L. The system mainly runs ok with the exception of the Rad in the loft that only seems to heat up when the the boiler goes to lockout. I do the normal things like bleeding the rads to ensure that air isn't building up etc.
I have had the boiler's circuit board replaced and thermistor. The system has just been thoroughly Power Flushed and a magnaclean has been fitted.The air separator was also looking manky so it was removed and converted into an H plan configuration.
When the system was originally installed no bypass was fitted which seems to act as a heat sink which could be contributing to the lockout problem. This is a funny one. I think it could be an air lock but I'm scratching my head to be honest. Any thoughts??
It could be air in the system, any air in the system could cause the boiler to go to lockout/overheat.
"the Rad in the loft that only seems to heat up when the the boiler goes to lockout." the boiler may be overheating, the excess heat may get to the radiator in the loft - as heat rises, you need an RGI to find out why the boiler is overheating
Who fitted the radiator in the loft, where is the tank in relation to this radiator ? did it ever work ?
Yes, the loft rad used to work and was working after the power flush was carried out not so long ago. The HW tank is located on the floor below the loft (its a flat) along with all the other rads. The F&E tank is the highest point of the system in a storage area of the loft.
I have a an air release valve sited close to the HW tank but it is manual and only releases air when someone comes along and unscrews the brass nut. Should I consider an auto venting air release valve?
The rad in the loft was added some years after the CH system was installed so I suppose its on its own little spare so to speak but it worked fine for years. I think you are probably on the right track, it may well be an air related problem. Now that my tenants have turned off the heating(warm weather) the boiler no longer goes to lockout, that is to say HW is fine.
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