Potterton performa 24 DHW problems

[ronbot]

I had this combi boiler fitted to my 1 bed house, fitted about 3 years ago.

Lately DHW heating has reduced in efficiency. When I first got the boiler, if I turned on the hot water tap fully for the bath, I had hot water hot enough that it was only possible to hold my hand under it for a second or two.

Now, I have to substantially reduce the flow by turning the tap to the halfway position in order to get the really hot water.

I have carried out a thorough investigation of the boiler and carried out all service tasks (bar checking gas pressure) and everything seems to be working ok. I have also followed through the fault finding chart in the manual and all seems ok.

I just measured the flow rate from the hot tap at full power which is approx 9L/min. Boiler flow rates are quoted at 9.8L/min for 35 deg rise and 11.4l/min for 30 deg rise so I am within the spec.

Any ideas??

 

[namsag]

If your not getting a 35 degree rise(water is always colder in winter with a combi) could be a couple of things
plate heatex starting to get blocked up
makesure maintap at meter has not been partially turned off
Do the temp lights go all the way to 80 when just HW is on?

 

[ronbot]

Thanks for the prompt reply.

I understand the "hot water colder in winter" factor. The boiler has actually heated a lot better in the past when ambient temperature was lower than it is now.

Not even sure where the water meter is, i guess in the road somewhere??? I certainly haven't touched it so I would be suprised if someone had tempered with it over Christmas

I have checked gas and water valves were all in the fully on position.

So that leaves the plate heat exchanger. If I remove it is it possible to clean out?? I do have access to high pressure airline if that helps.

 

[namsag]

I meant main tap at gas meter

 

[ronbot]

Thanks yes the gas stop cock is fine, Ive double checked.

Ive read some more info pointing toward the plate heat exchanger. Im going to remove and clean.

I could easily beleive its that sort of problem as the boiler DHW heat has gradually reduced in efficiency over some time.

In addtion with the cover off when running there is definately more water rushing noise it that area (like there is a restriction).

Thats for your help.

 

[gas4you]

Does the ch flow pipe off the boiler get hot when you run a hot tap?

 

[Agile]

In addtion with the cover off when running there is definately more water rushing noise it that area (like there is a restriction).

Thats for your help.

You may mean that you can hear air in the water?

Check the auto air vent cap is just loose. It could also be blocked too.

That on its own is unlikely to be the problem though. It will be a blocked plate HE. You can confirm that by measuring flow and return temps and there should only be about 15°C differential if its not blocked.

Tony

 

[ronbot]

Ok I have taken out both heat exchangers. Both had a bit of crap in but nothing too bad. Certainly no blocks. I flushed out on an external tap (mains pressure). Before I refit, is there anything else I should check??

 

[Agile]

Its difficult to see most of the blockages in a plate HE and they dont come out much with water flow.

You really need acid to dissolve it but that can be dangerous!

Shaking water in in out from the heating flow port will often get quite a bit out but its still no substitute for acid cleaning but might help as a temporary repair.

For the record I did not ask or encourage you to remove the primary heat exchanger which should only replaced by a gas qualified person.

While drained did you check the pump impeller for any dirt in the eye?

Tony

 

[ronbot]

"Its difficult to see most of the blockages in a plate HE and they dont come out much with water flow.

You really need acid to dissolve it but that can be dangerous!

Shaking water in in out from the heating flow port will often get quite a bit out but its still no substitute for acid cleaning but might help as a temporary repair."

Understood, however I would say they both looked in good condition inside.

"For the record I did not ask or encourage you to remove the primary heat exchanger which should only replaced by a gas qualified person."

Also understood, it seemed quite straight forward in the manual and was ok actually. Whilst I am not a qualified gas person I am a qualified engineer CEng so I would like to think I can apply myself to most mechanical stuff.

"While drained did you check the pump impeller for any dirt in the eye?"

Didn't check this but I think I am now at the point of giving up and calling a heating engineer. I only thought I'd have a look as I can usually fix most things mechanical and I really hate paying for something that I could do

Thanks all for the help