Combi boiler not firing up for hot water

[skotl]

Hi all

having a problem with an "Alpha CB28" combi boiler. Central heating is fine and so is, most of the time, the hot water.

But, every so often, it seems not to sense that we're trying to draw hot water and won't fire the burner (not sure of terminology here, of course).

If you can see this picture;

Untitled

• skotl
• 19 Mar 2013
• 1

what happens is that the lamp "B" will flash every few seconds but not illuminate. If I turn the "Selector" knob to its right, to "reset" and let go then most often you'll hear the burner igniting and the lamp "B" will come on and stay lit. After a few seconds we'll get hot water and lamp "B" will stay on until a few minutes after the hot tap is turned off.

Pressure when cold is around 1.2 and there are no obvious airlocks in the radiators (not that I know whether that affects the water). Never any problems with heating not coming on when expected.
We had a plumber in to fix the shower a few weeks ago and when we asked him he simply said "it will need a new boiler".

The fact that it works most of the time, and that a reset will kick the hot water into life, makes me suspect that it's repairable (by a heating engineer, not by me).
Any thoughts?

Many thanks
Scott

 

[ianmcd]

most likely the DHW diaphragm and there is a service kit available but dont be surprised if your engineer suggests a complete diverter valve as the kit can be a bit of a job if you havent done one before and some engineers prefer to replace the complete unit, I think the fact that you are resetting the PCB is just coincedence to be honest but it could possibly point to something else an experienced Alpha engineer will find this an easy enough fix

 

[skotl]

Brilliant - thanks Ian!

I don't mind paying for the whole kit as it still sounds much cheaper than a new boiler

Any recommendation on finding an alpha engineer? Just off of the http://www.alpha-innovation.co.uk/ site?

 

[ianmcd]

there are a few good ones in Edinburgh but sadly not allowed to advertise on this site, try Alpha themselves and ask for a fixed price repair, they were talking about doing that for £150 but not sure if they ever started it to be honest but if they do then take it the valve is more than that, if you cant find anyone then PM me and I will tell you some but cant do that on the open forum Im afraid.

regards

Ian

 

[skotl]

Brilliant - appreciate it - I'll give them a buzz.

Thanks again

 

[andysummers86]

Hi all,

I am having similar problems to this. Just wondered if a solution was found?

Thanks in advance,

Andy

 

[skotl]

Hi Andy

laziness / inertia meant that we haven't done anything about it. One point of interest is that, having been in the house for 2.5 years, it seems that it is only an issue in the winter (when you need it most!). During summer, there is not a problem and the hot water flows on demand.

Is this the case with yours, too?

Scott

 

[andysummers86]

Hi Scott,

I only moved into the property at the end of March so cannot really comment on the Winter months as it was quite mild in Leeds this year.

However it seems to have been fine up until about 2 weeks ago when it has suddenly started with this problem.

I have noticed that if I run the kitchen tap for example and it does not fire leaving it running and using another hot tap in the house sparks it into action.

I'll try get a friend round who's a plumber see if he can find a solution. Not a massive problem just more a pain that its not always working correctly.

 

[skotl]

That's interesting - your symptoms re the kitchen tap matches mine. The kitchen and the bath tap seem to be the worst.
Does clicking the reset button on boiler panel help?

Weird that yours started going bad as the weather improves, but mine gets better when the weather improves!

The lazy me would be delighted to hear how you get on, if you don't mind

 

[andysummers86]

Only tried the reset button once and it helped for around a day.

Like i say though its that random I'm not that sure it was the reset that did anything.

To be honest I don't really use the bath so can't really comment on that but the bathroom tap seems to be fine 99% of the time just the kitchen that is hit and miss.

Maybe mine will get even worse when the weather goes cold again?

Out of interest do you switch to hot water only during the summer months or just leave it switched to hot water and heating and just leave the thermostat off?

 

[skotl]

I'm in Scotland so we do still have the heating on, but only for a few hours each day.

I don't think that whether the heating is on or not makes any difference to whether the hot water is going to work on demand.

 

[Terry7556]

just had a look at alpha cb 28 on the search facility and diverter valves/diaphragms seems to be a common fault, as well as scaled plate heat exchangers
if you are not sure what to do i suggest start with a service and then get the other problems sorted out as a follow on to that

 

[ALCPlumbing]

The diaphragm must have split. This is why it operates when you open another tap as the increased flow of water is able to push the diaphragm which in turn operates a microswitch which tells the boiler there is a demand for hot water and it will fire up.
You could ring alpha for a fixed price repair or call a decent engineer if you know one. Just replacing the diaphragm shouldn't be too expensive.