Potterton Combi 80 Hot Water

[bav]

Can anybody help ? I have a Potterton Combi 80 Combi Boiler (not Puma) and the hot water keeps going hot and cold. An engineer has visited the boiler and changed the Diverter Valve and the Air Flow Switch.
He has taken out the water input restricter as he said the problem seemed like the water pressure was to low. The problem is still their and the hot water is still only 1/2 as powerful as the cold water.

Can any body advise on what it could be ? Could it be the Heat exchange unit ?

 

[chrishutt]

Could it be the Heat exchange unit ?

Yes, the secondary h/e could be clogged up with corrosion products (sludge).

 

[ChrisR]

Or the tap water side blocked with limescale? Hard water?

What is the hot water flow rate - it shouldn't be as high as the cold - unless that's v poor!

 

[croydoncorgi]

Chris - don't forget the bizarre diverter system on the Combi 80 and Puma restricts the hot flow until it warms up.....might be relevant, although I can't see how with a new diverter valve, apparently.

 

[gazthepottertonengineer]

Could it be the Heat exchange unit ?

Yes, the secondary h/e could be clogged up with corrosion products (sludge).

dont think so as this boiler only has one heat exchanger

More than likely scaled up as they are very prone to this

 

[Mikeyboy]

Very common problem on this boiler , is that the auto air valve , fitted to the top left of heat exchanger , becomes blocked and therefore inoperative .To ensure that the heat exchanger is fully vented of air ,slightly loosen the fixing nut , below the A.A.V. Be careful , as the boiler is under 1 bar of pressure.Carry this out when the HT. EX. , is cold.If air vents when you do this , you know the the air valve is faulty.