HW runs fine but CH won't work. Programmer fault?

[Tommo25]

My hot water system works OK, but the central heating doesn't switch on. I tried to switch the CH on using the programmer the other day (after months of it not being used during the summer) and there was no response and certainly no heat to the radiators.

It's a pressurised hot-water system and it's 6 yrs old. I have a Megaflo tank, Worcester boiler, two Drayton ZA5 2-port diverter valves, Grundfoss circulation pump, Drayton LP722 dual-channel programmer with a Drayton RTS1 manual (i.e. non-digital) thermostat next to it. The hot water comes on automatically each morning and evening (via the LP722 programmer) or when it's manually switched to "On". Either way, the red LED light on programmer illumates, the pointer on the side of the Drayton ZA5 valve moves from the "A" (closed) to "B" (open) setting, the Grundfoss circulation pump starts running and I can get hot water from the taps. However, the central heating does not come on either via the timer or when manually switched to "On" via the LP722 programmer. When I try to switch the CH on via the LP722, the LCD display on the programmer moves the pointer downwards to the "On" setting, but the red LED does *NOT* illuminate and nothing else happens i.e. the Drayton ZA5 stays at "A" (closed) setting. Similarly, although I've set the thermostat to a high setting and back it doesn't make the usual clicking sound. I thought the problem was the 2-port valves. However, the valve spindles rotate freely when the electrical servo motors are removed. Also, when I push across the black override levers on either of the ZA5s (to manually open valves for a few secs) it triggers the microswitch inside which starts the Grundfoss pump running for a few minutes. I have removed the programmer and the thermostat face-plates from the wall and cleaned the pin-contacts behind them, but it makes no difference. Incidentally, the pressure reading on the red expansion vessel is OK. Am I right in suspecting that the problem is caused by a faulty LP722 programmer which simply needs to be replaced? Or could something else being stopping the central heating from working?

[D Hailsham]

When I try to switch the CH on via the LP722, the LCD display on the programmer moves the pointer downwards to the "On" setting, but the red LED does *NOT* illuminate and nothing else happens

That's the clue.

As you suspected, the programmer has had it - at least the CH channel has.

As you have a mechanical thermostat it might be a suitable time to think of replacing it with a programmable digital stat, such as the Honeywell CM901/CM907. The LP722 could still be retained to handle HW times only.

PS Using a large typeface won't get your question answered any quicker and may even put some people off.

[Tommo25]

Many thanks for the prompt reply. You've confirmed what I suspected and your help is greatly appreciated. I'll order a replacement Drayton LP722 programmer asap. I will also look into getting a programmable digital thermostat to replace the analog type that's currently installed. Thanks again for your help.

[D Hailsham]

If you are thinking of getting a programmable stat for the heating there is no need to replace the LP722; the HW channel can still be used.

Assuming you get a wired prog stat you connect as follows:

RTS1 - New stat
L ----- Live
3 ----- Switched Live
N ----- N (if required) if not, make it safe in a terminal block.

At the LP722, move the wire in terminal 4 (CH ON) to terminal L.

[thescruff]

PS Using a large typeface won't get your question answered any quicker and may even put some people off.

I couldn't even read it, it made the eyes go funny. Think it needed breaking up into paragraphs

[Tommo25]

Just in case anyone was wondering how the story ends...

I eventually replaced the existing Drayton "LP722" dual-channel programmer with a new one (bought on eBay for a nice price) and the CH system works fine now. Obviously, this confirms that the old programmer was faulty and needed to be replaced.

Whilst I was at it I replaced the bog-standard Drayton "RTS1" room thermostat with a British Gas "ES1", which is a rebadged version (i.e. clone) of the Drayton RTS5 energy-saving thermostat. I wanted a thermostat with an identical footprint to the RTS1 because available space to fit it is very limited. The ES1 room thermostat was "new old stock" and I bought it on eBay for just 8 quid including postage. To put things in perspective, Wickes charge 22 quid for the RTS5. While the ES1 isn't a programmable thermostat, it's a definite improvement over the old RTS1 once you get the hang of its delayed-action features.

As an unexpected bonus, the new version of the LP722 has a back-lit screen (unlike the previous one), plus there are 3 (instead of 2) on/off programs, and the push-button controls don't have a "spongy" feel like before. So, I'm happy.