I've got an Ariston combi that's worked brilliantly for about 4 years but recently, I've had a problem with the pressure rising to between 3 and 4 bar (I'm constantly having to drain some water to stop it tripping the safety shut down). The dhw is flowing hot for about 5 secs then cold for about the same time.
Turn off cold water and run the heating - if it still rises and the combi fill is disconnected then it's probably the expansion vessel needs recharging or replacing.
If the pressure doesn't rise with the cold water turned off - then it'll be the cold water mixing with the heating water, through the plate heat-ex or combi fill etc/
ALDA and htg engineer,
Thanks for the replies. I recharged the expansion vessel the pressure is now ok - but my dhw still runs cold. The burner kicks in but shuts down after a couple of secs before kicking in again.
Anymore thoughts please.
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