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Posted by Geoman on February 2, 2007, 10:20 am
> We have a hot water heating system where this winter every morning in
> cold weather the pressure rises to around 30 psi and water gets dumped
> on the floor from the pressure release valve. It was originally an old
> gravity system with old-fashioned expansion tank - about 10 years ago
> we got a new boiler and they replaced the expansion tank with one of
> the smaller compression-type tanks and added a circulation pump. But
> we still have big oversized pipes and radiators.
>
> The mysterious thing is that the pressure during the day stays in the
> high teens and 20's and there is no leak, even when the water temp is
> fairly high - say 170 deg. The overpressure only happens in the
> morning when the system has been running hard bringing up the temp
> from the 55 deg we set it for the night.
>
> The plumber first replaced the pressure release valve. That had no
> effect. He then replaced the expansion tank - problem continued. Then
> replaced the expansion tank with a bigger one, as he felt the small
> one was undersized for the house (couldn't understand how it had
> worked for 10 years without incident, though - thought maybe that
> there had been some air in the radiators acting as an additional
> expansion tank). Still not fixed.
>
> I'm wondering if there could be an intermittent leak in the water
> refill valve when the system has been running for a while - can't be
> a continuous leak as the pressure does go down to around 15 when the
> system is cold. Plumber is quite skeptical - claims never to have seen
> such a thing.
>
> Any ideas?
>
> Peter
>
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