combi boiler heating water when cold taps used

[HelenB]

Have a baxi combi instant 105HE. When turn any cold water tap on fairly hard and then off again it is is triggering the boiler to heat water. Only just started doing this. Wondered if could be an issue with mains pressure or air in pipes as sounds coming from mains feed pipe into boiler almost suggest that water is being drawn back when cold taps turned on. Does anyone have any idea what might be causing this and is it serious? No fault lights are coming on and it is heating water normally otherwise.

 

[diverdee]

sounds like you have air in a hot water pipe somewhere or a dead leg of air that is compressing .when you turn the cold tap on you are reducing the pressure at the boiler allowing the water to back flow and fire the boiler for a short while

 

[lagunaglen]

you could fit a non return valve on the cold feed before the boiler which should stop this happening due to pressure fluctuations.

 

[HelenB]

Thank you. Have tried getting all the air out of the pipes but maybe some still trapped. Will have another go but if not the non-return valve sounds like a plan.

 

[Paul Barker]

Rest assured the boiler won't fire. The pump runs the fan might even come on but the burner won't light. So this is costing you vertually nothing.

The use of a single check valve adds problems of it;s own. it will quite likely squeel certainly squelch and might even set up resonance in your pipes.

Your dead leg is where the airing cupboard used to be.

 

[Agile]

you could fit a non return valve on the cold feed before the boiler which should stop this happening due to pressure fluctuations.

I recommend fitting the non return in the hot water output pipe after the boiler so that any expanded water in the boiler can expand back up the supply pipe.

Tony