intermittent fault with downstairs rads

[abidal]

My friend has an old c/h system (not combi). Occasionally his downstairs radiators "go off" for an hour or so and cool down. The upstairs rads are fine. After an hour or so the downstairs rads "come back on" and heat up ok.

Any suggestions on what the cause might be. I thought it might be a faulty pump, but if that was so then I would expect the downstairs rads to be cold at all times, not work intermittently.

Any suggestions would be gratefully appreciated.

 

[Burnerman]

Are there thermostatic valves fitted onto the rads?
John

 

[abidal]

No TRV's on the system.

Cheers,

Abidal

 

[namsag]

Old system.... Possibly pumped heating gravity hot water....
Room stat reaching temp shutting pump off so downstairs rads cool down till temp drops and roomstat brings pump back on ... Upstairs still heating because anti gravity valve is passing when boiler still firing for HW