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Three bedroom house with radiator c/h. Boiler Potterton RS 50/15 Well serviced each year. problem started 5 days ago, working fine up to then.
Room thermostat working normal, circulating pump cuts and heats all radiators as per normal. Above the boiler which is in kitchen is bathroom with a radiator this normally is always hot when the boiler is on, and still is, however the bedroom radiators normally stay cold unless the thermostat and circulating pump cut in, but five days ago without the thermostat or pump cutting in the bedroom radiators only are hot all the time, and consequently the boiler is coming on more often, why and how are the bedroom radiators getting hot without the thermostat or pump sending a signal? Would appreciate any suggestions. Mike Devon

is it gravity hot water system? it may be the anti-gravity valve getting stuck open

eggers wrote:is it gravity hot water system? it may be the anti-gravity valve getting stuck open

Eggers, Thanks for the reply, System is 36 years old, there is a small cold water tank in loft which feeds the radiators, alongside this is a somewhat larger tank which feeds the hot water tank in airing cupboard, so I am presuming that it is a gravity fed system.
There are 2 3/4 copper pipes between the boiler and the hot water cistern in the airing cupboard, there are 2 1/2 copper pipes between the boiler and all the radiators, where would I look for the anti-gravity valve in the system? Regards Mike.

Subsequent to my last post, the pipe sizes that I gave were incorrect, should have been 1" and 3/4".
I have since found what I think is a one way valve on the outward line of the radiator 3/4" pipe, maybe this is where the fault is, I shall replace it.
Only remains for me to say thank you to those who have contributed to this discussion and to express my appreciation to this site.