Worcester Greenstar 25i head scratcher

[KingDoey]

evening all.

Called out to this boiler late last night. No HW.

Pressure was down so checked expansion vessel etc and topped up. Hot water demand fires boiler which lights and then quickly reaches 97 odd degrees before shutting down. Get an initial blast of hot water through the pipes then just goes cool.

Heating working fine. First thought was the diverter valve stuck but would expect to feel some heat on the primaries if that was the case.
Have changed a few plate hex on the 24i juniors in the past but in those cases the boiler was firing and producing lukewarm water, not overheating. So make me think not that.

Haven’t ever really had any probs with these boilers so does anyone with a bit of knowledge of them have any thoughts?

Boiler only three years old so will probably be a call to Worcester Monday morn to get them out under warranty.

Cheers

 

[Millsy 82]

Check the pump. 9/10 over heat on hot water on these will be a weak pump.

 

[Scott_D]

If you put it in service mode does it stay on?

 

[ShaunCorbs]

Check the pump. 9/10 over heat on hot water on these will be a weak pump.

Heating would be effected tho wouldn’t it ?

Op I would check the plate temps in and out could be blocked / restriction

 

[KingDoey]

If you put it in service mode does it stay on?

Yeah put him in service mode, I believe diverter goes to mid position on these boilers. Still no hot water. Just blasts down the heating pipe work

 

[KingDoey]

Check the pump. 9/10 over heat on hot water on these will be a weak pump.

Pump was spinning fine. As I say heating working fine

 

[Scott_D]

Yeah put him in service mode, I believe diverter goes to mid position on these boilers. Still no hot water. Just blasts down the heating pipe work

Sounds like the pump is ok then

 

[KingDoey]

Blank reply there mate...

 

[Scott_D]

Can you check the diverter in the menus on this model?

 

[Millsy 82]

Heating would be effected tho wouldn’t it ?

Op I would check the plate temps in and out could be blocked / restriction

Not really on hot water it will run 25kw on heating it will be 20kw or less. So as I've said 9/10 it will be a pump

 

[ShaunCorbs]

Not really on hot water it will run 25kw on heating it will be 20kw or less. So as I've said 9/10 it will be a pump

But will be more resistance on the pump with heating on than hot water

 

[Millsy 82]

But will be more resistance on the pump with heating on than hot water

Not really though will it. A plate heat exchanger has very narrow water ways which will cause more resistance on hot water side in my opinion.

 

[Burger]

Is it worth checking the resistance value on pump and try and stop with a screwdriver?

 

[Mastermixlee]

Have you had the boiler in max fire mode (chimney sweep/service mode) on ch and testpost-1054067.rature rises on that?

Screwdriver check through pump bleed point?

If pump is fine on checks and doesn't rise excessively on ch demand then likely to be plate heat exchanger.

Ive had loads of em, and also there's been a fair few similar faults described on this forum.

Good Post to read which sounds similar is this

https://www.ukplumbersforums.co.uk/threads/worcester-over-heat-on-dhw.108291/page-2#post-1054067

Alot of back and forth but ended up being the plate heat exchanger and was solved using the f5/f3 cleaning method.

 

[KingDoey]

Thanks for all the info. Was the plate hex in the end. Boiler was flushed out and it was replaced. All gravy now

Thanks all

 

[billski]

Thanks for all the info. Was the plate hex in the end. Boiler was flushed out and it was replaced. All gravy now

Thanks all

And it was only 3 years old? Does it have a magnetic filter on the return?

 

[billski]

Thanks for all the info. Was the plate hex in the end. Boiler was flushed out and it was replaced. All gravy now

Thanks all

And it was only 3 years old? Does it have a magnetic filter on the return?

 

[KingDoey]

And it was only 3 years old? Does it have a magnetic filter on the return?

Yeah it does mate but probably wasn’t flushed properly when installed