Mechanical programmer clicks on/off repeatedly when HW on

[fingres]

I have an old mechanical programmer, British Gas branded but I can't see a model number or find similar pics on Google images.

The timing controls work fine and CH & HW come on at the right times, etc. However, quite often (but not always) when both CH and HW are on, the unit will click on and off every second or so. The CH and HW lights will also go on and off.

If I slide the HW controls to OFF it's fine. If I leave it on, clicking away, it still makes hot water.

When it's clicking, the boiler remains on, so it's not the boiler turning on and off.

I guess it's probably the programmer on it's way out, but wanted to check first whether it could be anything else? Dodgy thermostat on the HW cylinder perhaps?

Any ideas or advice gratefully received!

 

[fingres]

Any ideas?

 

[gas112]

Its a faulty clock ,cant be cylinder stat as the clock gives power to that and not vice versa

 

[fingres]

OK, thanks, so guess I'm going shopping for a new programmer. Just wanted to be sure.

Thanks again.