Baxi Due-tec Combi HE freezing up

[geofflove]

Hi
I have one of the above which is now about 3-4 years old. It is located in our garage.

When still under warranty a couple of year ago we had two occasions on very cold nights where the boiler froze.

We awoke to no heating/HW and the boiler displaying a low pressure warning E119. The gauge was showing 1 bar+. On each occasion I applied a hair dryer to the heat exchanger for about 15 min and suddenly the error code cleared the boiler restarted and all was fine again.

An engineer came on each occasion after the event. I believe both the pressure and temperature sensors were changed. He suggested that the temp sensor was giving odd readings. Since this we have had no problems - of course we were never sure if it was cured or if it just never got that cold again....

This morning. It was about -7C outside over night and I again awoke to no heat. Same symptoms. Same solution. All's fine again presumably until the next cold spell - which might be tonight.

I understand these boilers have a frost protection system to prevent this. It's clearly not working though. Can anyone suggest what might be at fault? Anyone had this problem and cured it?

Thanks

 

[geofflove]

By way of a further question...

The manual states that if the system temp goes below 5C frost protection is trigged and boiler fires on its lowest setting until thr system temp reaches 30C.

Am I right in assuming its the CH water temp sensor that is used to monitor this or is the DHW temp sensor? Or both? When frost protection is triggered is it just the boiler that fires or should it also activate the CH pump?

Might help me narrow things a bit....

Cheers