Hot, hot water, but no radiator heat

Chippy01

A friend called me today with a heating connundrum.
He has gas fired central heating and when he turns on the gas boiler it's supposed to heat up the hot water cylinder and the radiators.
The trouble is, it heats up the cylinder and when the cylinder gets hot it shuts down the boiler. At this stage the rads are barely luke-warm.
If he tries to over-ride the shut down to heat the rads, the cylinder will boil.
The only way he can get his rads to heat up properly is to drain the hot water from the cylinder down the drain.

Has anyone come across this sort of problem before? And if you have, how did you fiix it so that the cylinder and the rads heat up properly?

dilallio

I know nothing about gas fired systems, but it sounds like his circulating pump is not working.

Mongarra

Don't see how letting hot water from cylinder down the drain will heat rads. Maybe air in system. Try bleeding rads and if air comes through valves keep bleeding until water squirts out without any air.

Have to warn - I am no plumber but it happens me occasionally with oil-fired system and the bleeding of rads works.

TPM

depending on how the system is piped, there could be a balance valave on the return pipe(the bottom one) from the not cylinder, if this valve is open too much the heat from the boiler passed through the coil in the cylinder and back to the boiler again practically by passing the rads and causing the exact situation you describe.
It could also be caused by other things including sticking motorised valves, sludge build up in the system, air lock, faulty room stat.