Boiler not responding to timer

[Dean]

I have a potterton boiler and a Danfoss SET 5 timer. The timer controls CH and HW seperately.

Wit the timer, both CH and HW use the same set of 3 on/off timers (24 hour period) but you can then set HW and CH independently by settung setting either to 'allday', 'auto' or 'off'. Auto follows the 3 on/offs and 'allday' is on at ON1 then only goes off at OFF3.

The problem is the boiler does not seem to respond to the timer. It is staying on. The whole CH/HW system was installed by British Gas and has worked fine for over 10 years.

If I open up the radiator thermostat/valves when the timer says off, the boiler ignites and the respective radiators heat up. The timer appears to operate correctly in itself (LCD responds as expected when the buttons are pressed.

Also the boiler responds to the thermostat on the boiler itself. I can force it on or off by turning up/down thermostat.

I have homecare 200, but before calling them up, I was wondering if this is likely a timer fault and if so any checks I could make to confirm this. I wouldn't be surprised if my homecare doesn't cover the timer too. If I can pinpoint timer as the culprit, I'm assuming it is fairly straight forward wiring in a replacement, especially if I can get similar model timer.

Does this sound like a fault with the timer? I'd appreciate any advice.

Thanks.

[Owain]

When you say "radiator thermostat/valves" do you mean the valves like this:

which case, the way many systems work is the timer controls the valve motor. The valve motor is mechanically linked to microswitches which call for heat from the boiler when the valve actuates. If the mechanical link to the microswitches is stuck then the system will be stuck on or off and not respond to the timer.

IE there is no direct electrical connection between the timer and the boiler.

Owain

[OG]

Call out Homecare 200 - They should be able to give you a definitive anwer and if they include timer replacements (I would expect them to), you'll get it replaced.

If they don't include timers, you'll find a range of timers available at most DIY sheds for reasonable prices (£35 - £70) so you should be able to find one that works for your way of life.

I've only done one timer replacement, but so long as you keep careful note of which cables connected to what in the old Danfoss timer, you should be able to instal the new timer with little trouble.

You may want to look at replacement timers anyway - I know we ought to reset the heating settings if we're away for the weekend, but changing the timings is such a faff on our current (digital) one that it's never worth the effort and I think we ought to replace it with one of the mechanical ones with timer wheels.

[Dean]

I haven't checked the terms properly but I have a feeling that what is covered is very specific and quite limited IIRC. I guess I can still call them out to diagnose the problem, then if it is the timer, fit one myself. I think we have only had to call them out once in over 10 years. I wonder what will happen to the premium after a call out?!

Thanks for the help.

[Dean]

No, they are same kind of thing as these pictured on the left:

a form of valve as far as I know.

[John Stumbles]

Relay contacts stuck?

[OG]

If you've had homecall for the best part of a decade you've probably paid well over a grand; so it's time to get some value back - and if they increase the premium tell them to f-off.

We've had some version of homecare for nearly 20 years, and it's a fixed price deal - we've had a couple of radiator replacement due to leaks, one (or two) pump replacements and the usual handful of thermocouple failures over the last 18 years but never had a significant hike in annual premiums as a result.

[Owain]

Just a valve for that radiator. It would appear the pump is running continuously, which still points to a stuck actuator microswitch, and when the radiator valve is opened the system temperature falls below that of the boiler 'stat and the boiler operates.

Owain

[Dean]

OK, Thanks for the pointer. Presumably boiler and pump are controlled by the same microswitch, otherwise it seems that two switches would have to stick/fail around the same time, which seems unlikely. Where would be the location of the microswitch? Are we talking inside the timer itself or is it at the boiler?

I'm going to call British Gas but am curious as to what is going on. I don't want to approach it totally clueless even if I won't be doing the work myself!

Cheers.

[Roger Mills]

But do you also have any motorised valves similar to those shown in Owain's link? If so, you should have two - one for hot water and one for central heating. These valves are controlled by the timer and by the relevant thermostat (cylinder stat for HW and room stat for CH). Inside each valve actuator is a microswitch which closes when the valve is open, and which switches on the boiler and pump.

If one of these valves (the CH one in your case) jams open - and fails to close when the timer tells it to - it will keep the boiler and pump running. This exactly matches your symptoms. I would be amazed if the timer itself is faulty.

[Owain]

It's inside the actuator valve, which may live inside/near the boiler, hotwater cylinder, or under the floorboards somewhere.

Owain

[Dean]

That was the problem in the end. HW was stuck half open, probably been like that for some time. The CH one was electrically faulty. Both have been replaced by British Gas with new Sunvic zone valves.

Thanks to all for the advice.