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:
We replaced our boiler in Feb (new cast iron Ideal 15kW boiler).
System is fully pumped with 2x zone valves (one for heating, one for
water). Pump is on lowest speed (in airing cupboard next to a bed,
anything higher and it makes a loud whirr which is too noisy).
Everything has been working great, the boiler is nice and quiet and
had no problems with it. Heating on 24/7 on programmer and
controlled by programmable thermostat. Water comes on twice a day,
morning and evening for about 1 hour. The problem is that now with
our warm weater the room stat is always above the temperature
required - so only water is being heated. When this happens the
boiler starts making banging noises. I understand this is probably
locallised boiling of the water due to the water flowing too slowly
to extract the heat out the exchanger fast enough.
I have some pipe thermometers on the flow + return of the boiler and
boiler is set to 2nd highest setting. I can't remember the exact
temperature, but they around 60-70 degrees.
If the flow is too slow when heating water only, I believe the
problem lies in one of the following areas:
1.) Zone valve not opening fully (I've moved the manual opening
lever and that moves fine, but I don't know if that directly moves
the valve, or not)
2.) 'Balancing' valve fitted after zone valve not opening fully
(I've tried opening it fully by turning it and it appears to open,
but makes no apparent difference).
3.) Pipework is blocked, sludged or furred up (system was flushed a
lot before boiler replacement, including removing each rad -
inhibitor present, and certainly has been for last year prior to
boiler replacement, ie all the time we've lived here). However, no
similar problems with heating circuit - both circuits T off after
the pump to their respective zone valves. Therefore blockage must be
only within heating circuit.
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.
What are the actual flow and return temperatures?
I'll try and check these and get back to you.
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?
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.
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).
I was asked to call in at a good customer's house today, for exactly the
same sypmtoms.
In this case the kettling is due to the a 14 year old cast iron boiler but
the kettling goes away with the incresased flow rate when the heating is
on. We have agreed that I will add some noice reduction gel into the
system.
If you have elminated all the possible problems then I suggest you do some
or all of the following:
1) Increase the pump speed for the summer (OK it makes a noise but the
boiler is only likely to do a few 20 minute cylinder reheats in the day at
most.)
2) Open the 15mm bypass valve a little bit for summer only. Or replace
with smart bypass which open a bit in HW only mode.
3) Add a tube of Fernox Boiler Noise Reduction Gel into the system. (Tubes are c.
£30) IIRC. 8-(
Turning the boiler thermostat down might be counter productive if
it makes the reheat time extended.
In general 'heavy' kettling (cf. light wheezing) is a feature of boilers
with cast iron heat exchangers and can happen even from new.
--
Ed Sirett - Property maintainer and registered gas fitter.
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