On 5 Nov 2003 03:09:33 -0800, (Tim) wrote:

OK,

I am wondering if my motorised valve might be the problem... please
see point 2 below.

Last w/e I went out and bought 2 litres of non acidic descaler, added
these to the system via the header tank (perhaps my system is not
sealed as per your definition Ed!) and flushed it through to make sure
that the descaler got into circulation. I also gave all the rads a
good bleed

The banging continued ( I am not sure how long it takes for the
descaler to work but presumably a while as it will only work on
contact = thick layers of deposition will take a while to go).

Couple of days ago I bit the bullet and fitted a replacement pump -
got a Grundfos Alpha+ 15-50 as every one seems to think they are good
here. The noise has definitely reduced. Now there is perhaps one
bang (was 3/4) and no or little pipe groaning building to the bang.

However there is still a bang. Diligently I sat by the boiler at 6.30
this morning waiting for it to come on and notice two things

1) When it did come on there was one medium bang and then it sounded
like the water flow through the system really took off (lots of
whooshing)

2) Before the heating came on the HW circuit was energised but not
running yet (HW tank stat was not calling for heat) All the pipes
were cold (ie bolier had not run) BUT the valve cover and body was
really hot - say 45C or so yet the water temp in the pipes was
ambient. Would you expect the valve to run hot like this? can the
valves fail in this way and...could the valve also be responsible for
making the flow sluggish on system start up hence the banging???

Thanks again for all your response - very much appreciated

Tim

They do run a little warm when active, simply because the motor is
powered in a stalled condition to hold the valve open.

It's possible that the valve is sticky through being crudded up or in
general due to age. You can test this by removing the head and
checking how easy it is to turn the spindle.

However, unless the flow were really being restricted, I don't think
that this directly relates to the boiler banging.

I just looked through the earlier thread now, and I think it would be
worth doing a check as to whether the heat exchanger has a build up of
assorted sludge. This tends to create local boiling in the exchanger
and hence the noise. Is it a cast iron type of exchanger or low
water content (i.e. tubes)? I think that I would work out a way to
flush it through. I'd also take a look at a radiator to get an
idea of whether there is significant sludging in the system in
general. If you are thinking of adding TRVs, then it makes sense
to do a thorough clean out at the same time.

While you have the system drained down, you could fit drain cocks and
lever ball valves to either side of the boiler to be able to isolate
it and also to be able to hook up hoses to flush it through. If you
do this, I would add two further things. First of all a pressure
release safety valve on the boiler side of any valves, and secondly a
strainer on the return side to catch any circulating grot.

Given the circumstances, I would probably consider taking the heat
exchanger off and outside and flushing it, simply so that it could be
inverted - especially if it's a cast iron one - but obviously this is
a more significant job.

You could also consider doing a power flush - the equipment and
chemicals can be hired. BG and other contractors will charge an arm
and a leg for this and it's a gamble as to whether it's satisfactory.

Also, I think you need to consider the age of the boiler. It is
getting towards the end of its useful life and if you end up having to
do power flushes or heat exchanger replacements then the costs are
going to add up quite rapidly to the point where it really is throwing
good money after bad. I wouldn't spend any more than £100-200 on
fixing this.

In a boiler of that vintage, especially cast iron, it is going to have
an efficiency of 65% or less. If you replace with a new condensing
boiler, you can achieve 90% efficiency ratings to the SEDBUK seasonal
model. In practice, it's possible to achieve something like 25-30%
gas savings. I did such a swap a year ago and have achieved this.
So once you consider the mounting maintenance costs (in time as well),
plus the saving to be made in swapping the boiler; the actual real
additional outlay becomes quite small.

Personally, unless you can achieve an easy fix, I would dump the
boiler and concentrate on cleaning up the rest of the system and
fitting the TRVs.

..andy

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