Ongoing Issue with Worcester 20/25 combo boiler

[MikeMacMiller]

Hi Folks

We have the above boiler in service currently supplying central heating with no problems but the hot water is very intermittent after 2 or 3 minutes running it is cutting off then back on shortly after.

The mother board relays can be heard clicking on and off,

we have had heating engineers on site who changed the board out, the flow switch is brand new, the diverter valve was replaced a year ago and the boiler has been serviced regularly.

Any ideas as our engineer appears to have given up?

Cheers

Mike

 

[Tea-Break]

Hi Mike,
I assume this is the Heatslave.
Does it make any difference if hot water only is selected (heating off)?

 

[Rob Foster]

Hi Folks

We have the above boiler in service currently supplying central heating with no problems but the hot water is very intermittent after 2 or 3 minutes running it is cutting off then back on shortly after.

The mother board relays can be heard clicking on and off,

we have had heating engineers on site who changed the board out, the flow switch is brand new, the diverter valve was replaced a year ago and the boiler has been serviced regularly.

Any ideas as our engineer appears to have given up?

Cheers

Mike

How old/new is your naughty
20/25/WB ? you can quote the serial,number if you can see it
centralheatking

 

[SJB060685]

I have attached an image of the wiring flow chart. This is easy to follow if you know how. I take it this is happening when calling for water at taps and not to heat store? From what you’re saying this sounds like relay 4 is energising then de-energising, cutting power to burner and pump. This could be a dodgy relay, connections to relay or maybe a bit of crap stopping flow switch from making contact intermittently.

 

[Tea-Break]

The OP says the ‘board’ has been replaced. I assume he refers to PCB. This would mean the relays are all new and still producing the same fault?
You are of course correct in your approach. But it is unlikely that the new board would have the same fault.
As ever there is no substitute for being on site with multimeter in hand!
Check stat, flow switch, then diverted valve. My money is on the diverter actuator.

 

[SJB060685]

Without wanting to sound like a c**t I disagree. The PCB has been replaced, relays with it but that doesn’t mean it’s not faulty. It could be a refurbished PCB that itself is faulty. If you look at wiring flow chart and know that the diverter will return to HW naturally then you will see the diverter is already in position. Looking at the flow chart you can see power will come through flow switch, which will activate the relay, this in turn supplies power through the boiler stat and limit stat to burner, at the same time the pump will be energised, heat for HW will then be generated. If I was there I would be testing for live back from flow switch at the point of burner cut out. If we still had a live from flow switch we know that is ok and I would be suspicious of the relay.

 

[SJB060685]

If the actuator was stuck wouldn’t this create the end switch and just supply additional power to pump? When HW is called for shouldn’t relay 4 break power to diverter valve?

 

[Tea-Break]

No response from O.P.
SJB: I can if necessary post the fault finding sequence to test PCB (which should only be carried out by a competent person, as involves 230v live testing).
Not trying to be clever here, just helpful.

 

[SJB060685]

No I understand Tea-Break. Yes please post it so I can at least have a look. Of course this should be carried out with competence, so hopefully OP wouldn’t have a go unless has a good understanding of electrics. I’m not trying to sound clever either, rather than us debate we should try to solve this collectively, rather than against each other. The only reason I said the above was because if you follow the electrical flow chart and bare in mind the OP was saying he could hear relays clicking at point of HW failure then you can trace feeds or lack of it upto the relay and further. Of course I might be wrong. Please share this info so I can study further

 

[Tea-Break]

1: Test for voltage on PCB (Black block connector- pin 1, from left.
2: Test pin 3, on lower block connector left side of PCB. (No voltage- indicates blown fuse)
With 230v established at both above. Select H.Wtr on from timer or rocker switch.
3: Test pin 2 on same block conn as above (voltage here proves timer or rocker switch OK)
4: Test Hot Water Stat: A’s marked on PCB. (If voltage is not present- Test and or replace Hot Water Stat , If stat is OK, replace PCB.

Sorry unable to scan or link, as from an old Worcester training manual.

 

[SJB060685]

No worries. Thanks for that, however the installation and service manual I have saved gives all the information an engineer needs. Yes it requires looking at a couple flow charts but you can trace everything and know what to check on each pin and wire colour where, which is easy for someone like us as we know how to do these things. Having said that, like you say the OP hasn’t responded, so I’m still unsure whether it’s when there’s HW demand at taps or the heat store, both of which require different testing. Sorry if I sounded like a t**t, I’m still only young, I don’t have decades of experience like some but these flow charts are easy to follow when you know how, which clearly we both do.

 

[SimonG]

Is it the built in clock on this boiler? If so I would be looking at that and replacing with an external clock. Had this a few times.

 

[Tea-Break]

It’s frustrating, not having any response from the OP.
Why seek help/advice on here and not bother to check progress?

 

[SJB060685]

It is frustrating yes. I suspect however that because the boiler is fine for CH and only intermittently playing up for HW then OP isn’t too bothered. Maybe I’m wrong, or maybe another engineer has helped and had more success than the previous. Perhaps we’ll never know lol

 

[SimonG]

It's the norm on here.

very little feedback from ops