Potterton EP2002 programmer problem?

Hi all, I recently moved house and have inherited a central heating system of mixed age. The boiler (Worcester-Bosch Greenstar) is quite new - the original 10-year-old Suprima having apparently given up the ghost - but the controls are still as they were for the Suprima. There's a Potterton EP2002 programmer, and a Honeywell wall-mounted master thermostat (not sure of the model). There are also thermostatic valves on most but not all of the individual radiators.

The new boiler is great when all works according to plan, but I'm finding the control system temperamental. It comes on with the time clock first thing in the morning, and completes its first timed period OK, but with the programmer set to TWICE the system is then very reluctant to come on again in the afternoon/evening when the time clock switches on for its second timed period. The red CH and HW lights come on OK, but the boiler doesn't fire. It isn't the thermostat overriding the programmer as I can adjust that so it's set well above where the thermocouple clicks.

Sometimes the boiler does come on again but at an arbitrary time, unrelated to any time clock settings. Sometimes I can bring it to life by pushing the sliders to on the programmer to OFF and then back again to one of the on settings. Yesterday in desperation when none of this worked I powered the EP2002 off at its mains supply and back on after 15 secs or so, and bingo on came the heating.

[Incidentally the same seems to happen if I set the programmer to ONCE but turn the heating off mid-morning by turning down the Honeywell main thermostat; the boiler doesn't appear to fire up when the thermostat is turned back up later in the day. So far the most reliable method I've found of having the heat on tap come the evening is to leave the programmer and the main thermostat alone, and to cut back the heat output in the middle of the the day by adjusting the radiator valves: this does work (after a fashion) but it's not a satisfactory long-term solution.]

I am no expert but this all feels like a programmer malfunction. Should I just accept that at 10 years old I'd be better off replacing it? And if so, what with? Are Potterton programmers more reliable nowadays, and/or is there a different market leader? From other threads in this forum I gather that it should be possible to swap in another Potterton programmer with minimal effort as they all have a compatible backplane; but that installing a different programmer would be considerably more effort. I'd be most grateful for any advice.

You must have some other controls near your hot water cylinder and they need checking.I doubt that your programmer is faulty,but if it is then EP series are a straight swap.To change for another requires a rewire as EP's were sometimes used as a wiring centre.

There is a small removable panel on the top of the EP2002, that when removed, allows you to test the 'heating on' terminal to see if its live. If the heating is on on the programmer, but the heating won't work, if you put a test meter on this therminal you can find out if its powering the system or not. If its dead, then it will be the programmer thats faulty.

If you want guidance on identifying the terminal, let me know.

Consider upgrading to the EP6002. It will attach to the back plate without needing wiring alterations. The main benefit is that you can seperate out the hw and ch timings, so they don't need to be together.

Thanks, both, for the advice thus far.

45yearsagasman: Such as an intermittently sticking valve, or something similar? I had to do the power-off/power-on routine for the programmer again last night, but as previously it did the trick. So it's beginning to look as though whatever the cause of the problem is, it does get reset by this process.

Whitespirit66: I'll try to do that check today. If my meter hasn't gone AWOL in the house move, that is ...