Baxi duotec showing DHW temperature as 90deg

Nas · Jan 13, 2015

Been called to repair a baxi duotec 33he. The display is showing the Water temperature going up to 90deg and switching the burner off. until the temperture drops and fires up again...and keep going in this loop.
The water is not that hot i put my hand under it its def not 90deg its about 60deg. Also I could hear water inside the boiler as if it was boiling inside
Would a temperature sensor cause this? or a problem with the heat exchanger. The heating seems ok.

Any help appreciated
Nas

kris · Jan 13, 2015

Hi Nas, did you check the resistance accross the DHW stat just to see if its within its parameters ?

Billy Bob Bob · Jan 13, 2015

if ch is ok plate heat is blocked,try cleaning it

Nas · Jan 13, 2015

Thanks for the replies. I suspect its the heat exchanger but ive not checked the thermistor yet to confirm its ok.

arran197 · Jan 14, 2015

The temperature displayed on the boiler is from the primary flow sensor on the flow from the main heat exchanger. It sounds like it could be 2 problems. It could be the diverter valve passing and could also be the plate heat exchanger blocked. More than likely both.

Turn the ch off and make sure it's cold. Open the hot tap and feel the flow pipe, if it gets hot you know that's the issue and you need a new diverter valve. If it's not getting hot, then it'll just be the plate. It's not too much trouble to check it though, isolate the boiler and drain the water out, undo the 2 screws on the manifold to release the plate and you can swing it out. You might need to take the motor off the diverter valve to get it out. Have a look inside and clean it. If it's totally blocked it will need some strong cleaner in it or replacement

Millsy 82 · Jan 14, 2015

I would say blocked phex especially if you can hear it boiling inside. I had 1 with a dodgy primary thermistor but that worked ok on the dhw bit heating wouldn't work at all. The primary thermistor works as a high limit stat when the dhw is called for