WORCESTER 24cdi combi intermittent problem

[warehouseman]

Tenant is having occasional problem with Worcester 24cdi boiler. 9 year old combi, works fine normally, pressure good. When one of them showers say for 5 or 10 minutes, and then someone else goes in to have a shower shortly afterwards, they cannot get any hot water either from the shower or any taps. They wait for about 10/20 minutes and then try turning on again and miraculously it works. This happens about once a week but sometimes it can run ok for days. It only seems to happen occasionally when people take a shower one after another. Is it overheating / is it a safety cut-out or should I call an engineer out ? Someone said it might be a diverter valve problem - is that difficult/expensive ? or a diaphragm problem ?
Has anyone seen this type of problem before ? Of course, when i call someone out it will be perfectly ok !!

[htg engineer]

Could be the diaphragm is split or stretched, this can cause intermittent problems, and at times of high demand - more taps being used etc (not necessarily in you house, could be next door) the water flow/pressure can be reduced that it's not enough to push the diaphragm up.


htg

[warehouseman]

That or the diverter valve has been mentioned to me before. Not an expert, so got Brit Gas in under agreement. They said it must be something else other than diverter or diaphragm. Asked me if the tenants adjusted the shower flow to increase/decrease temperature. This missed the point really as the boiler works perfectly fine for 95% of the time. Other hot taps in the house didn't work and the boiler occasionally didn't fire up.
Obviously intermittent faults like this are hard to trace.
So what they have done is reduce the water flow from 23litre per min to 13, saying the pressure seemed high. I will have to see if this alters anything.

[eggers]

24cdi's don't have diverter valves i don't think, i think they have a dual heat exchanger, which would lead me to the flow switch, or the flow switch filter.
i had a similar fault on this boiler and it turned out to be the fan, not sure if that helps

[warehouseman]

As the problem continued a few times each week, I've got closer to identifying when it happens.
If someone takes a 10/15 minute shower, the boiler works fine. Then, if another person takes a shower within 2 or 3 minutes, then things are usually fine as well. HOWEVER, the problem arises when someone tries to take a shower 15/20 minutes after the last person. At that point, the boiler DHW demand indicator light comes on but the Flame detection indicator light fails to come on & the boiler fails to ignite & provide hot water to any shower or tap in the house.
Wait another half hour, & all is fine again.
Any ideas ?

[htg engineer]

As you have a service agreement with BG get them back again and again and again - you pay for it so they need to sort it.

The 24cdi does have a diverter - get the diaphragm checked. If it was overheating it wouldn't just start working again - you would have to reset the boiler.

If you look at the top of the diverter, there'll be a microswitch, the pin comes out to operate the microswitch when you open any hot water outlet - next time - check has the pin come out enough ? press it up with a screwdriver - boiler flashes up ? diaphragm is split or stretched, doesn't flash up ? could be faulty microswitch or PCB fault

htg

[eggers]

which worcester am i thinking of then? hmmmm probably the 24i RSF
well, if it's not the diverter valve it could be over heating, along the lines of the pump, dhw sensor or auto air vent

[htg engineer]

I've worked on a few 24cdi's and I'm 100% sure it has a diverter. I have also worked on others (without diverter) but not sure of the model I think it might be the 24i RSF Junior.

If the boiler was overheating it would have to be reset, warehouseman is saying if left alone - it'll work again later on.


htg