Heating suddenly always on - timer fault?

[Showerman41]

Our CH system is controlled by a Honeywell ST1501 7-day timer, part of the system when we moved in back in 2014. The house was built in 1997 so I guess it's the original timer. We had the boiler replaced two years ago (Baxi EcoBlue 16) by a local plumber who also did the annual service in November. The thermostat in the hallway is a Drayton Combi-Stat.

Last night the hall radiator was much hotter than it should have been an hour after the timer was set to switch it off. Checking the timer showed OFF for both CH and hot water (Sadia MegaFlow). It was obvious this morning that the heating had been on all night; checked timer again and it still showed OFF. However, the boiler's green light was on and I doubt it should have been. I've now switched off the timer's power.

However, while checking settings this morning I found a label referring to a battery. I can't see any obvious panel for a battery and I've done a websearch and (not surprisingly) can't locate a user's guide.

Can someone tell me
1) If it is common for timers to fail?
2) How I get to the battery if it is actually needed on a mains-operated timer?

Thanks in advance

PS - No point calling our plumber now. It's not an emergency, just an inconvenience that can be worked around, and he is a very wise man who insists weekends are for his family :yesnod:

PPS: I owe you all an apology. I just looked back at my earlier thread (2013) and realised I never came back to complete it. Unfortunately, my wife was made redundant and I had already retired, so a lot of plans fell by the wayside. Sorry!

 

[Gasmk1]

if it has a battery this will just be a back up battery for the program i think you will need to get your plumber/engineer out as it sound like maybe your zone valve is faulty, unless you have a frost protection thermostat which may have kicked in

 

[Showerman41]

Thanks - I've emailed our boiler man.

 

[Showerman41]

Thanks - I've emailed our boiler man.

 

[king of pipes]

As above the zone valve or valves is the place to start, you could try different switching times for heating and hot water that may determine which channel is at fault on the programmer if the problem is there.

 

[Showerman41]

Thanks for the responses - our man must be away since we've not had a response by either email or text and he's usually pretty reliable. In the meantime, after its strange day, the heating has been working properly. Thinking back, the boiler exhausts through a north-facing wall and there was quite a strong cold wind that day, so my (layman's) speculation is that may have triggered the frost-stat??

In the meantime, when our man gets back to us we'll have a chat to him about it anyway, and ask him to check the zone valves (there seem to be two in the airing-cupboard system, going on Google illustrations).

 

[king of pipes]

Glad your back up and running bud , inconsistent faults can be a pain to diagnose please post the outcome regards k

 

[Showerman41]

Sorry I haven't got back sooner (how time flies!). Plumber never got back to me but we've had no problem since my original post... I'm now touching wood

Thanks anyway - if there are further developments I'll revive this thread.

 

[moonlight]

It probably was a zone valve and you may have the same problem again in the future. They sometimes stick, even more so if your system isn't clean.