Any boiler experts on? Boiler firing up for water but not for heating...

[Bettyhatesavocados]

Can anyone give any insight? It's not a combi. It's just a regular boiler. It's set to come on for water and the pilot light's coming on for that and the water's getting hot and the pilot light's then going out when it should. The heating's just put on as required (not often but would be needed more in the coming months) but when the slider is set to 'constant' to switch it on, the pilot light's not coming on/ firing up and the display shows a zero which means nothing is happening...
Anyone got any idea why the pilot light would come on for the water and heat it up but not for the heating? Seems weird. Any insight would be appreciated. Hoping it's nothing crazily expensive to repair.

Thanks!

Do you have a three-way value in your system as shown? If so it could be a problem with this, maybe it's sticking? If these stick then when the programmer instructs the boiler to turn the value on for heating the valve never fully opens and this can stop the boiler from firing.

The fact your boiler is coming on and working normally for hot water would indicate it's not a problem with the actual boiler.

It been a while since I worked on these systems so maybe someone with more recent experience can help some more.

Thanks very much for replying, TobyHouseMan. No idea if it has one of those... The front's not even been off or fear of making things worse. If it is that, would you know if that means the whole part needs replacing or can the stuck bit be unstuck some how? I'm guessing it'd need a gas safety registered engineer to repair or replace.
Hoping you or someone else might be able to chip in wrt how much it should cost to fix or replace...
Thanks again!

It's really difficult to know how much it will cost to fix without knowing your exact system and what the actual fault is.

If you have this value then its normally where your hot water cylinder is, but not always. Have a look around there and see if you can see it. Reply with a pic if you can find it.

If it is this value then these normally cost around £80 and fitting would take something like 1/2 -1 day of a plumbers time depending on if the system needs draining down.

There are other things it could be. If it were a programmer fault then a cheap one of these starts from around £70.

Good luck.

Tagging @PigletJohn who is good at this sort of stuff.

Indeed @PigletJohn would likely be much more use here.

Hi TobyHouseMan... Thanks. 'm probably going to sound ridiculously naive and ignorant here but are you saying (at an average rate of £80 from limited research) it would be 6+ hours of a working day x £80 plus parts to sort? Eek! I appreciate your help.
Hi SpongeBobJudgeyPants thanks for tagging PigletJohn. Hope he sees it and chips in! Thanks so much for your help!
Ps. Don't know if it changes anything but the weird thing is... if the water and heating are put on 'constant' together, the heating comes on too! But it won't come on independently! But, obvs, you don't always want the water and heating on at the same time; sometimes you just want the heating on cos the water's already hot!
Thanks all!

Have you turned up your thermostat, just to be sure it is calling for heat?

What temperature is the room thermostat on your wall set to?

photos of your timer/programmer, room thermostat, boiler, cylinder, and all the things around your cylinder that have cables would be useful.

I have the opposite problem - we have to have the heating on for the water to heat... even in summer! But actually if we turn the thermostat down low the water still heats without the radiators coming on. We had someone in once to look at the problem but they never fixed it.

Hi PigletJohn, thanks for chipping in. Can't show pics at mo - using a friend's PC and don't have pics. The wall thermostat was set to 17 (and has never been an issue before). Tried new batteries in the thermostat and still the same. Pushed the wall thermostat to 20 and still the same so turned back down to 17.
Not sure it makes a difference but the heating is not set to come on when the temperature dips below the temperature the thermostat is set to. The heating just goes on as and when necessary by using the constant feature (ie put to constant for an hour or two and then to off). Never been an issue before.
The weird thing is the pilot light won't come on/ boiler won't fire up for heating but will for water (water is set to come on each morning for an hour or so). However, if you put both water and heating on to 'constant' the heating will come on too, just not independently of the water (which you obviously don't need and don't want to pay extra for if the water's already hot).
Thanks for your help.
Ps. InescapableDeath: that must have been a nightmare in the summer till you realised you could turn the water temperature lower and still get hot water!

Are you sure you don't need the hot water on for the heating to be on? I need to have both on for my heating to work, but can have my hot water on without my heating.

I reckon TobyHouseMan is right and it’s your diverter valve. It’s usually one of the cheaper things to fix.

Hi Chocoqueen Yes, sure, cos the heating has been on in the past loads of times without the water being on too. Thanks, though.
WongKindOfFace The three-way valve thing? I read that a diverter is for a combi and that's usually a sign the system's knackered. This, thankfully, is not a combi, just a regular boiler so I'm hoping PigletJohn is right and it's one of the less expensive things to fix. A new boiler would be out of the question.
PigletJohn Will have a go at getting pics and posting them on the thread, probably tomorrow or Tues... thanks so much for helping. It's really appreciated!
It's so hard to find a good gas engineer too - usually rely on recs from family or friends but no recs this time. Thanks again.

I had something similar and it turned out my thermostat was battery operated and the battery had died! Two AAs and the problem was solved. If you have a wireless thermostat it is worth checking.

Sorry, PigletJohn, the wall thermo is set to 17. It's always been fine. Upped it to 20 but no difference. Batteries changed, still no success...

I've had a similar problem in the past and it was the thermostat.

Thanks, Latenightreader, but it's a on dial type one. Did change the batteries with brand new ones but still no success!

I had that problem once but I solved it by switching the boiler off at the mains, leaving it for 20 seconds, switching it back on, let it reset itself and bingo, all was fine again. Think it must have just been a gremlin in the system!

Google faulty diverter valve. Really common fault. You can buy parts online and fix it yourself but if you're not confident I'd get a gas engineer to come and do it for you.

igotdemons It's worth a shot.Thanks! Have tried re-setting on the boiler itself but no success.
What I can't understand is that the heating will come on if it's on with the water. It's weird. You'd think if the heating won't work in isolation, it wouldn't work by putting it on with the water either...but it does. It's as if the heating is reliant on the pilot light coming on/ firing up for the water... Don't want to have to put the water on to have the heating on...and not sure what that would do to the system long-term anyway

We had the same problem a few weeks ago and it was the 3 way valve thingy- cost £120 to have fixed and 4 different days of waiting in for blinking engineers to not turn up .

Argh...Purplethrow Nightmare! It's so hard to know where to find a decent engineer who doesn't charge the earth. One bloke said 3 port valve (from description over the phone) and said £300 ish!

The chap who fixed mine called it a diverter valve? Anyway, I bet it’s the valve, whatever it’s called. Fingers crossed you can get it fixed quickly.

@Bettyhatesavocados

Argh...Purplethrow Nightmare! It's so hard to know where to find a decent engineer who doesn't charge the earth. One bloke said 3 port valve (from description over the phone) and said £300 ish!

British Gas do fixed price repairs but I’m not sure how cost effective they are?

Same thing happened to me with a normal vented boiler (not combi) and it was the 3 port diverter valve. Cost £120 to repair but boiler guy was here for other stuff already. I think the valve is about £80 on its own.