Hot water problem.
 

We have a pressurised central heating/hot water system run by a Worcester Bosch Greenstar 24i boiler coupled to a large 210l cylinder and the central heating side has been set to 'OFF' for a few months now so it's only hot water that is operational. For a few months now our hot water which we set to come on every day automatically hasn't always been getting hot as it should and has quite frequently required the use of the HW boost facility on the programmer. We didn't think too much about it and put it down to extra hot water usage by Osem Jnr until more recently when I discovered that the timed HW on/off periods don't seem to be getting the boiler to fire at all and the BOOST function is also intermittent. This is the weird bit - when this first started happening some months ago, in order to see if the boiler had conked out altogether I tried switching on the CH briefly via its boost function and the boiler immediately fired up as it should. Having confirmed it was still working I then cancelled the CH boost setting, waited about a minute and then tried the HW boost once again. This time the boiler fired up again perfectly and within an hour we had a tankful of very hot water. Last night we'd run a bath and I set the programmer for a 2 hour boost to replenish the tank. The light on the programmer came on as it should but I later found out that the boiler hadn't fired up and the water was stone cold. However, once again, by switching on the CH the boiler ignited and after cancelling that the normal process of controlling the HW via the boost function worked once again and we had hot water. Obviously if the hot water tank is still hot then the boiler won't ignite regardless of any programmer settings but I'd have thought that as we used up all the water it should have come on at some point when the water temperature dropped below a certain level.

I'm not intending to fiddle around with anything on the boiler but would like to have a clue what the problem is so has anyone got any idea what might be wrong? I changed the programmer for a new one of the same make which simply plugs into the same backplate to rule out programmer issues by the way. The problem appears to be the same with either programmer.

TIA as always.

:tu:

Re: Hot water problem.
 

Our boiler heats water on demand, so no hot water tank, but it too started to fail.

I noticed the central heating water pressure dial kept dropping so I had to add more water by the fill link.

I reported it, but nothing was done (council cuts).

I rereported it and the engineer found that the rubber bladder was leaking. That dropped pressure to the point the system would shut down both central heating and hot water.

The bladder is up against the wall so it meant a total stripdown....

Re: Hot water problem.
 

I know it's not the same type of system but I haven't had any pressure issues showing up on the boiler which has the only pressure indicator I can see.

Re: Hot water problem.
 

Slightly different system for us - pressurised central heating & instant hot water, BUT if the pressure drops too low on the central heating side then the boiler won't fire for the hot water but will fire for the central heating. The pressure has to get pretty low for the central heating side to fail. Check if all the pressures are where they should be - the central heating pressure will rise when you fire the central heating and this could be enough to allow the hot water side to function hence the behaviour you're seeing.

Cheers

Dave

---------- Post added at 16:22 ---------- Previous post was at 16:19 ----------



Well that's me out of ideas!


Cheers


Dave

Re: Hot water problem.
 

Next door has the same boiler as us, but it's in the upstairs landing airing cupboard, feeding a hot tank next to it. It often fails to run because they draw water so quickly out of the tank that the inflow can't refill the system in time. This causes airlocks which result in a lot of banging noises and hot water squirted out of the overflow pipe into their garden, followed by shut down as the system detects low water levels.

Re: Hot water problem.
 

Interesting feedback guys thanks. :tu:

I only turned the CH on momentarily, not long enough to heat anything, just a few seconds to see if the boiler would come on.
Then I turned the CH back off and tried the HW boost again and it worked straightaway. I've been able to repeat this procedure and it seems to work but I can't think why and it's not exactly ideal. :spin:

Re: Hot water problem.
 

Re: Hot water problem.
 

Cheers Taf, I chatted to the installer today and he reckons the motorised valve may be the problem here.

Re: Hot water problem.
 

Had exactly the same problem this morning. No HW but boost would not work. Cancelled that, set CH to boost, boiler fired up, turned CH off then set HW to boost and it worked. Hot water again... :spin:

The gas fitter is coming on Saturday morning so fingers crossed he can sort it out.

Re: Hot water problem.
 

Gas fitter came this morning, did some electrical checks and changed a motorised valve. Boiler fired up nicely and hot water was restored. Hopefully tomorrow morning the programmed timings will operate properly and we won't need to faff around with boost settings etc. Fingers crossed for now... :)

Re: Hot water problem.
 

YAY!

Re: Hot water problem.
 

Anyone care to guess how much it cost? :erm:

Re: Hot water problem.
 

£100ish for the valve and about the same for the labour?

Re: Hot water problem.
 

the plumber did it for free co's their good like that :)

Re: Hot water problem.
 

£175.00