Baxi Combi Boiler- short cycling

[aaronmaoeric]

I have a Baxi Combi Boiler. The issue is that the boiler turns on and off automatically in a period of every 5-10 seconds. The flame goes off and water starts to be cold, then it's turns on again and the water is warm(normally when temperature drop to 80 degrees centigrade it turns on). It's terrible while taking shower. But seems central heating work properly(keep turning on at 65 degrees centigrade)

Can someone please advice me what to do at this time of the year when it's so chilli. The advice and suggestions are much appriciated

Eric

 

[Deleted member 267285]

Morning Eric,

There’s a lack of information. Is this when running hot water? When the heating is on? Both? On its own?

 

[aaronmaoeric]

Hi Chris W,

This happens when running water, no matter on its own or together with heating.
In fact when I turn on heating together with hot water, the heating doesn't work until I turn off hot water. But then burner keep on.

Many thanks!

Eric

 

[Celeronmanuk]

I'd suspect secondary heat exchanger is scaled up.

 

[Deleted member 267285]

You have a combi boiler, and this is how they work, the heating is turned off unitl hot water is satisfied. What I meant to ask was, does it cycle with heating on as well? Which model of Baxi?

 

[aaronmaoeric]

Hi Chris,

For hot water, the cycle betweem on and off is frequenty around every 15 seconds, temperature between 80-95 degrees centigrade. While when heating it keep on for several minutes then off.
The model is Baxi Duo-tec Combi 40 HE

Thanks

Eric

 

[Deleted member 267285]

Ok so you probably have a circulation issue, and could very well be a scaled heat exchanger as suggested, make sure both flow and return valves are open underneath and no other restrictions are in place. Have your pump checked out as well.

 

[aaronmaoeric]

Thanks Chris, I reckon block in heat exchanger might be the most probable reason, now checking how to replace or flush, really appreciate your professional comment!

 

[Deleted member 267285]

If severely blocked, no chemical or flush will get rid of it.

 

[ianmcd]

with the CH switched off run a hot tap and feel the CH pipes below the boiler, is one heating up when it shouldnt ?

 

[Celeronmanuk]

You have the exact same symptoms as we had as far as I can tell. I tried sentinel x800 which improved things very marginally. In the end a replacement dhw heat exchanger resolved it. Old unit was well scaled up. Cost me £80 for the part and about £60 to get it fitted.

 

[aaronmaoeric]

Thanks Mate!