Combi hot water ebbs and flows

[Yankbo]

I have a Potterton Gold Combi 28 HE on a brand new system following full renovation. However I am unable to get a consistant flow of hot water to any outlet. The temperature holds as hot for around a minute before fluctuating between luke warm and warm.

Boiler has previously been sat in dry storage after light use in an office enviroment. House has 1 shower room and one kitchen sink.

Water pressure is around 2.7bar and flow is around 13lpm at boiler point.

During use the DHW temperature is set at 40 degrees but the boiler shows the temperature shooting to 80-90degrees, this happens at what ever temp the DHW is set to.

Please could you recommend steps to allievate this issue?

 

[cross thread]

Scaled up secondary heat exchanger would be my guess.

 

[Yankbo]

Thanks for the quick response. Is the secondary heat exchanger something i should look at trying to descale or replace entirely?

 

[cross thread]

Replacement of eBay about 25 quid easy to change

 

[MagicDoughnut]

The 80-90 degrees is the boilers temperature, not the HW temperature at the taps. That sudden increase in temperature indicates a blockage in your plate heat exchanger and the boiler is overheating. I wouldn't advise a DIY repair, get someone competent in. For the price replacing it is better than attempting to clean it.

 

[Yankbo]

Replaced the heat exchanger over the weekend and had my first consistantly hot shower since moving in! The existing exchanger it was completely gunked up on the DHW side.

Thanks again for the advice on fixing this!