Noisy new boiler when heating water only

[David Hearn]

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

[Andy Hall]

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

To email, substitute .nospam with .gl

[BillV]

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?

[David Hearn]

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

[David Hearn]

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.

[Andy Hall]

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

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

To email, substitute .nospam with .gl

[Andy Hall]

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

To email, substitute .nospam with .gl

[BillV]

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..

[Ed Sirett]

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.