On Tue, 08 Nov 2005 17:07:47 GMT, 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.
You probably don't have a fully pumped hot water system. The water is
heated by gravity (relying on the fact that cold water is heavier than
hot water, so hot water rises around the circuit. This happens in the
radiator circuit as well - which explains why the upper radiators are
hot while the lower ones aren't.

* How easy / expensive is it likely to be to replace the pump on this
'antique' boiler (getting someone qualified to do it that is)
The pump isn't in the boiler - it's a separate unit something like
this: http://www.screwfix.com/app/sfd/cat/...72726&ts=77549
That's easy to replace. 100 quid max for a plumber to do it.

* If I replace the back boiler, could I use a combi boiler but basically
keep the same hot water/ central heating setup. The back boiler
currenly heats water in a hot water tank in the airing cupboard.

There's no point. You can use a system boiler in place of the back
boiler and still keep the tank but the whole idea of a combi boiler is
that it heats water instantly as you need it. You'll get much better
showers from a combi, but if you choose a "cheap" one you might not
get the flow rate you want when filling up the bath.

* Are there any reasons other than aesthetic why I can't put a combi
boiler on the fire place using the chimney as a flue. i.e need to be
certain height above ground, thereby minimising changes in the plumbing
which is all currently situated there.

The flue needs to go outside - you can't flue into the chimney. Modern
combi boilers are room sealed appliances. They take the fresh air they
need for combustion from the flue.

I think it wouldn't be easy to get the flue all the way up the chimney
and out the top. There are maximum limits on flue lengths anyway
specified in the boiler's installation manual.

* If I went for a condensing boiler, other than finding a way to run off
the condensate, could this be situated on the fire place as above.

Chances are that you will be forced to have a condensing boiler. The
condensate output must fall at around 2 degrees or more to an internal
trap or external drain or soakaway. If you can't get the fall for
whatever reason you'll need a separate condensate pump which collects
condensate in a tiny tank and pumps it out when the tanks is full. A
big boiler might produce 2 litres/hour condensate.

Apart from the condensate I don't think there is any reason why you
shouldn't put the boiler on the fireplace.

Mr F.