or try searching for 'powermax 155 programmer' on eBay.
You can fit them yourself, but I would advise using a qualified engineer.
EDIT: forgot to say that, if you haven't already realised, you can still get hot water (not central heating though) by putting the three-position switch on the front panel to the uppermost position (marked with a shower symbol and 'Hot water cont.'). This by-passes the programmer, and makes hot water available 24/7; for that reason, you may wish to turn it off at night.
Last Edit: Jan 17, 2016 8:33:47 GMT -5 by northpole