Why can I only get hot water when the central heating is on?

[kasha]

I've got an ancient Ideal Standard E type CF gas boiler with pumped hot water and central heating which has worked well for many years. Through the summer the central heating is off and hot water is programmed in the 'once' option.

Last week the hot water failed to come on at all even when programmed to 'on' all day. I then switched the hot water to 'off' and the central heating to 'on', the heating came on and I got a cylinder full of hot water that way. Yesterday I fitted the recommended replacements for both the cylinder strap-on thermostat and the programmer but the problem with the hot water remains the same.

I can hear the motorized valve for the central heating click on and off but the hot water valve remains silent in all options. When the central heating is on the run of pipes to and from the hot water valve get hot. How can I establish if this valve is the source of the problem or something else?

I'm not able to replace the entire system at present.

 

[breezer]

(only a guess as i am not a plumber or heating engineer) most vlaves have a manual switch move this and see what happens, then check for voltage when some one lese changes the programmer settings.

you may be able to replace just the motor on the motorised vlave if it is at fault

 

[ollski]

probably because the microswich is shot in the hw valve so it opens the valve but does not transmit power to the pump and boiler wheras when the ch valve energizes the water is pumped around the still open hw circuit.

 

[gas4you]

Replace the hw valve actuator head.

 

[Bahco]

( i am not a plumber or heating engineer)

You're not a spellings teacher either

 

[kasha]

Thanks gents, you've confirmed what I thought was the problem with the valve being stuck in the open safety position due to lack of power.