sime 80 problem

[CLARKO]

hello,
sime 80 combi, c/h works fine when a h/w demand is made boiler fires for 30 secs then cuts out, relights after about 30 secs flow rate has slowed down ,h/w temp has also dropped from what it was any help would be grateful.
thanks

 

[kevplumb]

post it HERE

 

[meldrew's_mate]

Sounds like you have scale build-up (or other restriction) in the DHW heat exchanger.



Burner goes off because the boiler primary water is hot enough, heat flow through the exchanger wall + scale is slow so "hot" water comes out cooler, scale restricts water flow.

So get it de-scaled, then fit a scale reducer on the cold water inlet.