In an earlier contribution to this discussion,
angusclaydon wrote:

I currently have a baxi bermuda 551 back boiler central heating / hot
water system. It has a gas fire on the front
which is no longer used.

When I turned on the central heating - it's been off since last
winter - the there was no characteristic gush of water surging round
the
system and the radiators don't work, apart from one in the back
bedroom.

I bled the radiators, checked the valves on the thermostatic radiator
controls weren't stuck, but still no joy.

After looking at the boiler and reading some previous posts, I am
coming round to the idea that the pump is not working. The boiler
still heats water for the hot water system but it isn't coming on and
staying on for any period of time as it usually did when the central
heating was on. I can't quite work out why the back bedroom radiator
is working ok, unless water is reaching it via the ho****er system.

* How easy / expensive is it likely to be to replace the pump on this
'antique' boiler (getting someone qualified to do it that is)

As someone else has said, the pump is a stand-alone unit - not part of the
boiler. If the pump hasn't been used all summer, it may simply have seized
rather than failed completely. If you can find it, unscrew the endcap (very
little water will escape) and try to turn the shaft with a screwdriver. You
may be able to free it. If not, it is not too difficult to replace -
particularly if it has functional isolating valves either side, enabling it
to be removed without having to drain the system.

The pump is probably located fairly near to the boiler - it could even be
inside the chinmey breast, or it could be under the floorboards if you have
a wooden floor downstairs.

If an upstairs radiator gets hot without the pump running, it means either
that the radiator is connected to the gravity hot water rather than heating
circuit, or that there's *some* gravity circulation within the pumped
circuit, as sometimes happens.

If you *do* decide to replace the boiler, you will need a lot of plumbing
and control system changes to bring it up to modern standards - and meet
current building regs - and you need to find a more suitable location for
the replacement boiler.
--
Cheers,
Set Square
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