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Noisy new boiler when heating water only |
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| message from David Hearn on 19 May 2004 |
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.
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).
Any ideas?
Thanks
David
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| Andy Hall replied to David Hearn on 19 May 2004 |
4) The boiler is generating more heat than the cylinder coil can
absorb?
What are the actual flow and return temperatures?
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.
Is the boiler range rated? You could try reducing the burn rate if
so.
Otherwise, I think it might be time for a fast recovery cylinder.....
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.
.andy
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| David Hearn replied to Andy Hall on 20 May 2004 |
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.
I'll try and check these and get back to you.
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.
Nope, 15kW fixed.
Quite possibly - what's the sort of prices for these compared to normal
cylinders?
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.
Thanks
David
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| Ed Sirett replied to David Hearn on 20 May 2004 |
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.
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| Andy Hall replied to David Hearn on 20 May 2004 |
Yes but it's a cast iron boiler, so takes longer after the flames stop
to cool.
See if there is much of an overshoot in temperature on the flow as the
flames go off.
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
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.
.andy
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| BillV replied to David Hearn on 19 May 2004 |
Is there any kind of a bypass for the boiler, automatic or otherwise, when
all the TRVs shut?
e.g. non-trv bathroom rad before the valves?
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| David Hearn replied to BillV on 20 May 2004 |
On the heating circuit the hall radiator (where the room thermostat is) is
non-TRV. In the bathroom the TRV is set to max (when we arrived, it was the
only radiator with a TRV bizarrely!). So, that satisfys the bypass for the
heating circuit. At present, even in the hot weather we've been having, the
bathroom radiator gets hot, so I assume Max means no-thermostatic control
and fully open. No problems when running with heating only.
On the hot water circuit there is no bypass, but then there isn't a TRV so
that's not a problem. Problem occurs when running with hot water only.
The only issue I can see then is if the boiler fires whilst both valves are
shut/jammed. The wiring is such that when the boiler is on, at least 1
valve is open, so only the jamming situation is an issue. Is it normal to
have a bypass for jammed valves situations? Incidentally, there is a 15mm
pipe (whereas rest is 22mm) with manual valve (same as balancing valve after
HW zone valve) which bypasses both valves. I don't know what this is for
and has always been shut.
Thanks
David
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| BillV replied to David Hearn on 20 May 2004 |
Ahh, thats a manual bypass. Tricky to setup, it should be open a bit or
replace it with an auto-bypass valve; £25 from Screwfix , item 98894.
Your bathroom rad could have acted as a bypass if it was plumbed before the
valves.
Thats how all the houses around here were piped by the developer.
The bathroom rads get hot even in summer and they work as a bypass for the
boiler.
The only people who get problems are those turn off the bathroom rad
completely or fit a TRV.
Many modern combi/system boilers have an auto-bypass built in..
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| Andy Hall replied to David Hearn on 20 May 2004 |
That is a boiler bypass to cover the case when both HW and CH circuits
are closed off and the boiler has been firing.
Normally it should be open a bit. The boiler should have an
over-run thermostat to power the pump so that water continues to be
circulated away from the heat exchanger after the other circuits are
closed.
These can be improved by fitting an automatic bypass valve which opens
only when the pressure exceeds a certain value - i.e. both valves
closed, pump running.
However, none of these help if the pump setting is too low.
One other thing that occurred
Did you try running the HW with a completely cold cylinder? Also with
the pump on high? These would tell you if the problem has to do
with getting the heat away from the boiler.
Presumably you did flush the pipes thoroughly when you changed the
boiler and they are not full of sludge?
.andy
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