Worcester 24cdi RSF - Hot water demand

[warehouseman]

Have narrowed down an intermittent problem thats occurred for months.
When a shower is taken for say 10 mins, everything is fine. Wait 2 minutes & have another shower and things are USUALLY fine. However, if you wait say 15/20 minutes after the first person & then try getting hot water, the DHW indicator light comes on but the Flame detection indicator light remains OFF, meaning the boiler fails to ignite and no water can be got from shower or taps. Wait another half hour & everything is fine again. Obviously this causes problems in the mornings when people want their showers !
Any ideas ?

 

[aggis]

Think you need to know your lights combinations & colours, have a look at www.worcester-bosch.co.uk/.../installation-and-servicing-instructions-for-24cdi-rsf--discontinued-07.pdf

Intermittant faults can be a pain, but get as much as info as you can & talk to Worcester 1st, esp if you think it's the pcb.

 

[Puddle]

I would be looking at air pressure switch first,sticking

 

[RoryD]

Are you saying no water at all or just no hot water?

I'm thinking perhaps the water filter mesh is blocking

 

[fireblade]

I spent half a day working on one of these changed the board phoned worcester changed transformer worcester could not give me a answer it ended up being the multi plug on the left hand side of the boiler and it goes to the limit stat air pressure swith and the fan it was just a bad connection on the plug that was intermitent on the hot water hope this helps

 

[warehouseman]

Thanks all.
We're talking about 'no hot water'.
Almost always happens 15/30 minutes after someone has had a shower lasting 10/15 minutes. The DHW demand light comes on , but the flame light does not trigger and so only cold water comes out.
I already had the fault diagnosid chart, thanks, but it basically does not pinpoint the problem other than vague references that it could be the pcb - but it might not be !!

 

[aggis]

If you have a multi meter check resistance of dhw & primary ntc's. should
be 11k ohms or above cold
When it won't come on after hot water, the over heat might have operated, because the ntc is out of range

 

[RoryD]

Thanks all.
We're talking about 'no hot water'.
Almost always happens 15/30 minutes after someone has had a shower lasting 10/15 minutes. The DHW demand light comes on , but the flame light does not trigger and so only cold water comes out.
I already had the fault diagnosid chart, thanks, but it basically does not pinpoint the problem other than vague references that it could be the pcb - but it might not be !!

Check and see if the pin rises and makes the switch on the top of the diverter valve, if it don't then you need a service kit (and ALL the o rings u can get) to replace the diaphragm. If it makes then u need the microswitch

 

[Biglils]

Did you manage to get to the bottom of the Worcester 24cdi boiler which would not supply hot water after a shower but was ok after 30 mins as I have one doing the same and have done all the usual checks ?
It is as if something is heating up and then cooling down but the temp sensors are reading correct when the boiler will not fire up after the first shower !
Regards