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John Rumm John Rumm is offline
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Default worcester bosch boiler pressure

On 05/06/2021 20:58, wrote:
On Tue, 17 Nov 2020 23:33:02 +0000, John Rumm

It sounds like this is not a fault with the dial- its probably telling
you the truth. Its more likely that the system is losing pressure over
time for some reason.
The boiler is ten years old. Can it be fixed?


Should I be looking at a
new boiler?

Not if that is the only faulr

Apart from the pressure dial, the boiler is fine.

I expect the pressure dial is fine, and you either have a system leak,
or a non working expansion vessel.

With a leak, you would expect the pressure dial to act fairly normally -
rising a bit as the system warms up, and falling back to where it
started as it cools - however you may see a steady drop over a period.

If its an expansion vessel problem then the pressure change will be much
larger, swinging very high as the system heats, that causes the
emergency pressure reduction valve to dump some water out of the blow
off pipe outside. Then as the boiler cools it dropping to a much lower
pressure than when it started.

We had a British Gas engineer a couple of days ago, and he said the
loss of pressure over a period of two or three months is natural, that
the boiler needs to be topped up every two or three months, and not to
worry about it.

Is he right? I'm not into this stuff, should I worry?

If it has been recently drained and refilled (or its a completely new
system) then there will be a fair amount of air dissolved in the water.
This will tend to come out of suspension and accumulate in a radiator
somewhere. When you bleed that rad, you will drop the pressure a bit and
may need to top up.

However once a system has been running a while and the the water is
basically stagnant, then it ought not change much or at all.

It is possible to have tiny leaks in a system - so slow the water
evaporates before you ever see it. This is generally not a problem if
you only need top up once or twice a year. Although you should
periodically add some extra corrosion inhibitor since it will get
diluted over time, and the fresh oxygen introduced each time you top up
needs to be "mopped up" by the oxygen scavenger in the inhibitor which
will get used up by the fresh water being introduced.



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