Boiler does not turn on for hot water

robshak

Hi all,

Felt I conquered it all after solving the mystery of the phantom charges, now it is 2-1 to the boiler!!!

After the holidays (when the hot water was programmed to come on for 30 mins a day), the boiler has stopped turning on at all!

After some research, I have tried the following:

• Added pressure to approx 1.8 bar.
• Increased thermostat temperature to 25.

However, if I turn on both central heating and hot water (1 hr boost), the boiler kicks in, the flame light comes on and central heating comes on, but no hot water through tap.  Alas, as soon as I turn off the hot water at the programmer, the boiler switches off.

I noticed from the gas consumption that even when on holidays, though programmed, there was no consumption of any gas on some days indicating the programmer may have kicked in but the boiler did not come on.

Anything else I can try to trouble shoot before the hot spell is over (cold water is just fine now for shower :-)) and I have to call in an expert?

I have a Worcester Bosch boiler probably 8 yrs old.  I also have a separate hot water tank (but no cold water/expansion tanks). So not sure what system is this.

Thanks all in advance.

Rob

stuhse

If you have a combi boiler you should always have hot water, it just comes on when you switch the tap on.  Which thermostat have you set to 25 degrees ?  If its one on the boiler its possible you have set the hot water temp to 25 not the radiator temp.  There are usually 2 settings on a combi one for each.   This would possibly explain your issue. 

robshak

stuhse said:

If you have a combi boiler you should always have hot water, it just comes on when you switch the tap on.  Which thermostat have you set to 25 degrees ?  If its one on the boiler its possible you have set the hot water temp to 25 not the radiator temp.  There are usually 2 settings on a combi one for each.   This would possibly explain your issue. 

Hi, thanks.  I think the thermostat is for the central heating.  How do you control your hot water temperature? I have now added some photos of the set up so that you can see what I have.  There is a separate hot water reservoir..may be this is not combi at all, need to do my research..ha ha..any further suggestion?

mmmmikey

I vaguely remember having a similar issue and it proved to be a faulty diverter valve. I got a replacement from Screwfix and fitted it myself. Sorry I can't remember the details but if you do some research on diverter valve issues that may give you some clues. Hope this helps in some small way

[Deleted User]

If you have a combi boiler you should always have hot water,

There is a big clue in the photo of the unvented OSO hot water cylinder. The most likely reason is either a stuck zone valve on an ‘S’ plan or a stuck diverter valve on a ‘Y’ plan. You may be able to operate the valve manually. Valves can stick over time - particularly, if they are not cycled frequently. If the valve doesn't open then, irrespective of the programmer setting, the boiler will not fire.

robshak

mmmmikey said:

I vaguely remember having a similar issue and it proved to be a faulty diverter valve. I got a replacement from Screwfix and fitted it myself. Sorry I can't remember the details but if you do some research on diverter valve issues that may give you some clues. Hope this helps in some small way

I have been researching too.  One anomaly though, my boiler does not turn on at all even when tap is turned on (or when the programmer kicks in).  I don't think it is heating water at all!  If there was hot water and it was only failing to divert it to the tap, faulty diverter makes sense.  Did your boiler turn on upon activating tap? Thanks.

QrizB

robshak said:

mmmmikey said:

I vaguely remember having a similar issue and it proved to be a faulty diverter valve. I got a replacement from Screwfix and fitted it myself. Sorry I can't remember the details but if you do some research on diverter valve issues that may give you some clues. Hope this helps in some small way

I have been researching too.  One anomaly though, my boiler does not turn on at all even when tap is turned on (or when the programmer kicks in).  I don't think it is heating water at all!

You've got a hot water tank, which is unusual for a combi boiler.

If I was to guess, I'd say that the boiler is emulating a system boiler and the HW tank is heated by the CH circuit as a separate heating zone - S plan or Y plan, as Dolor describes above. If this is the case, there won't be anything connected to the HW output from the boiler.

I agree that the most likely diagnosis in this case is a stuck valve or a failed tank thermostat.

robshak

[Deleted User] said:

If you have a combi boiler you should always have hot water,

There is a big clue in the photo of the unvented OSO hot water cylinder. The most likely reason is either a stuck zone valve on an ‘S’ plan or a stuck diverter valve on a ‘Y’ plan. You may be able to operate the valve manually. Valves can stick over time - particularly, if they are not cycled frequently. If the valve doesn't open then, irrespective of the programmer setting, the boiler will not fire.

Thanks. Just flicked the zone valve away from auto towards right on photo.
while water on, still nothing..the programmer was on 1 hrs boost. It just winds with whining noise...now put it back to original position.

FreeBear

I would suspect the thermostat on the tank has failed - Possibly behind the nameplate below the two white cables ?

Be careful if you remove that panel. Any exposed terminals are likely to be at mains potential.

One comment - 30KW boiler just for central heating and a hot water tank !!! You probably only need ~14KW unless you have a mansion to keep warm.

Krakkkers

Is the water hot or cold at the moment?

Reed_Richards

QrizB said:

You've got a hot water tank, which is unusual for a combi boiler.

I briefly modified my heating system so my combi boiler would serve a hot water cylinder as an extra heating zone.  This worked fine but my plumber had (superstitiously?) insisted on retaining one hot tap that was still connected to the combi output.  So you could find that one tap gives you hot water, or it might be none.