On Thu, 20 May 2004 09:42:25 +0100, "David Hearn"
wrote:

Andy Hall wrote:
On Wed, 19 May 2004 15:19:02 +0100, "David Hearn"
wrote:


4) The boiler is generating more heat than the cylinder coil can
absorb?

Surely though this would result in the boiler cutting out rather than making
banging noises? It happily cuts out when the temp is reached normally.

Yes but it's a cast iron boiler, so takes longer after the flames stop
to cool.


What are the actual flow and return temperatures?

I'll try and check these and get back to you.

See if there is much of an overshoot in temperature on the flow as the
flames go off.


Is the situation better if you totally empty the cylinder of HW and
then allow it be heated from cold? This increases the heat transfer
a bit and would be a clue.

It certainly does it in the morning when the water has cooled - but I don't
know how long it takes before doing it - again, I'll check and get back to
you.

Is the boiler range rated? You could try reducing the burn rate if
so.

Nope, 15kW fixed.

Otherwise, I think it might be time for a fast recovery cylinder.....

Quite possibly - what's the sort of prices for these compared to normal
cylinders?

It depends what you mean by normal. SOme of the older ones would
only absorb a few kW.

Have a look at http://www.albion-online.co.uk/superduty%20x.html



5) Is it possible that the pump is knackered? If you have it
driving a cylinder coil and all pipework is 22mm then there should not
be much noise even on high setting. Replacing with a Grundfos Alpha
might help.

The pump tends to make a grrr-grrrr-grrrr-grrrr-grrrr-grrr-grrr noise as it
runs which gets louder and increases in frequency when the speed is
increased. On slowest setting is it barely noticable, on highest, you can
hear it below, downstairs. It may be made worse by its position and how the
pipework is. I suspect that the pipework is resonating, amplifying and
transmitting the noise around the house. It is also located in the airing
cupboard about 6" from the head of anyone sleeping in the bed. Therefore
even a relatively quiet pump would be noticable in that situation. I have
suspected the pump may be an approaching problem (due to the noise) but it
does appear to be working fine (functionally) on both heating only, and
heating and hot water.

Could you put the pump elsewhere perhaps? Resonating pipework is
often an issue, but the bearings wear as well and the noise you
describe may be the onset of that.

I think I'd try to move it if possible.


At present I've wedged the heating zone valve open, so whenever the
water is heated, the hall and bathroom rads come on (rest are TRV'd)
and this removes the banging noise. I don't like this solution as
it means the heating zone valve never moves, and therefore
potentially could jam. It's not a problem at present and is working
okay - but ideally I would like to get to the root of the problem.
I don't want to alter the pump speed as any faster and it gets too
noisy, besides, it works okay on heating only (or heating and water).

Thanks

David


..andy

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