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Heating system expansion vessel

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Tim Lamb

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Mar 17, 2022, 2:36:47 PM3/17/22
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Covered before I know but this is from a different angle..

The internal vessel in my boiler is just about large enough to handle
the cold to hot system expansion: remaining between 1 and 2 bar.

However, there can be water hammer from (I think) the by-pass valve
opening during the change from DHW to underfloor heating.

To overcome this I installed a second (5L) vessel close to where the
by-pass is fitted. The installation instructions advise pressurising the
vessel to 1bar. Fine through the Winter but now we have some warmer
weather the water hammer has returned.

The boiler spends more time fully shut down as the roomstats are not
calling for heat. As a consequence, it is not uncommon for the system
pressure to drop below 1 bar.

My thinking is that I need to more closely monitor the cold system
pressure but also that the additional vessel pressure should be dropped
to something like 0.75 bar. (with the water side at zero.)

Any thoughts? (conventional chalet bungalow so no huge static pressure
concerns)


--
Tim Lamb

rick

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May 17, 2022, 7:03:11 AM5/17/22
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I have 3 pressure vessels .....
1 on primary loop
1 on Underfloor heating loop
1 on DHW

They do fail .... and you can only set pressure when unfilled - which is
a pain.
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