Combi starts up as cold water tap turns off

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Hi,

This my first post on your very useful website, so be kind!

I have just had a valliant ecotec 831 boiler installed and i have noticed that when cold water taps are turned off in the house (kitchen/downstairs toilet/upstairs bathroom) the boiler starts up, not for long, but then goes silent again.

From looking through the forums i have found similair issues. It sounds as though the cold water is being drawn away from the boiler, so the boiler's pressure/ flow sensor sees a change and starts doing something. People seem to suggest that a non-return check valve with a minature expansion vessel before the cold water inlet on the boiler should sort the issue.

That's fine, and i get that with the kitchen tap as it is approximately 2 metres away from the boiler, but will the upstairs taps also cause this to happen? Is the boiler sensor that sensitive?

Another theory is that dead legs can cause this to happen, becasue of trapped air? But i cant think logically if this sounds right? i have notice he has left a very long dead leg in the loft to the old header tank. Also i've notice an old galvanised pipe is also capped, which would have gone to the old galvanised tank.

My boiler instatller is trying to charge me for rectifying the issue, it seems to me like he should have checked this when testing the boiler and not left dead legs, which sounds like bad practice to me?!

Apologies for the war and peace, just trying to supply as much info as possible. Many thanks.
 
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I would tend to agree with the dead leg being the problem.
Whether it's down to your installer or you is between the two of you, I would suggest it depends what the quote/estimate says, eg, if it says disconnect old/redundant pipe he should have done so.
 
If you change D88 to 1 this may help. It changes the activation level to 3 litres rather than 1.5. It's all in the booook! Bo'selecta
 
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Thank you both for your replies. I'll give the D88 a go first. Cheers.
 

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