Replacing timer on an unusual central heating / hot water system

[dagnug]

Hello, I'm not a plumber but like to fix things myself where possible, and any help on the following would be much appreciated!

My sister has recently moved house and the gas boiler that does the central heating and hot water is not a system I've come across before... in the airing cupboard there's a hot water tank, a mechanical timer switch, and a unit with "off/timed/on" and "water priority/heating priority" switches. There's a valve that moves mechanically when changing between hot water and central heating, and obviously radiators around the house, and a room thermostat downstairs.

The mechanical timer has broken, and I wondered if it would be possible to replace the room thermostat with a programmable thermostat with inbuilt timer, such as the Honeywell THR870CUK to do the timing, if I leave the switch in the airing cupboard set to "on" rather than "timed"? (This worked for my combi-boiler at home.)

I think this would enable the central heating to go on and off at the set times, but would this also be able to time the hot water going on and off? Maybe this is beyond the limitations of the system anyway and the water just comes on when the heating does? I can't remember if the broken timer had separate controls for heating and hot water.

It may be I have to get a plumber in to replace the broken timer, but if changing the room thermostat for one with an inbuilt timer would fix the problem that's be great, as it's within the limitations of my skills! Or is there another type of timer that's relatively easy to install?

Many thanks,

Dan

 

[WHPES]

Yes a programmable thermostat such as the Honeywell CM907 will do the job of time control for the heating, but you will still need a timeclock for the hot water. Assuming the motorised valves are working OK you are probably best off calling an experienced electrician as the wiring can be complex for an amateur.