Water hammer from Hot water System

[willidh]

Hi All

I have been experiencing what I understand to be Water Hammer for many months now. The problem appears to be when the boiler starts-up first thing in the morning and in the evening - I get a loud bang from the pipes. It is definitely the hot water system as the central heating is off.

Many of the water hammer problems I have read about relate to people turning taps on and off. This is not my problem.

I have lived in this house for over five years. The problem has only been around for less than one year. The water pressure in my area is quite high as I live in a dip.

What can I do to further diagnose the cause of the problem, and hopefully fix it?

Thanks in advance for your help and advice

Danny

 

[chrishutt]

Sounds like it might be overheating of the boiler due to lack of flow. What boiler is it and is the cylinder circuit pumped or gravity?

 

[willidh]

It is a Potterton Suprima boiler. I believe the circuit is pumped.

 

[chrishutt]

Check that the pump is working and that there is enough water in the system (look in feed tank).

 

[willidh]

Thanks for your help so far.

I believe both are OK. The tank in the loft has water in it and the pump appears to work when the boiler is on. There are no problems with the hot water itself - there is plenty of it. The only problem is the loud bang in the morning and evening!

 

[chrishutt]

If it's one loud bang, it's probably explosive ignition. You need a Corgi guy to check that over.

 

[ChrisR]

If it is doing what we think, it will be affected by the position of the small temperature knob on the boiler. See where it is now. The banging might be worse with the knob turned right up, and possibly absent when on "1" or equivalent. Try it, as it would be a useful diagnostic.

Is this a repeated banging- several erratic bangs in as many seconds, or a single one...?

 

[willidh]

The temperature knob is already near to the lowest setting - I have turned it all the way down just to check.
It is a single loud bang - pretty sure it's the pipes - it might be coming from the airing cupboard - where the hot water cylinder is (it's a Megaflo)

 

[willidh]

Just had another big bang. Checked the boiler - it is off. However the pump in the airing cupboard is running.
Any ideas of the significance?

 

[willidh]

I spoke to a plumber on the phone, who unfortunately due to personal reasons was unable to come and visit to perform a diagnosis. Based on my description of the problem and my hot water system he said it is most likely to be that the motor in the Honeywell Powerhead is starting to fail.

How can I further diagnose that it is the powerhead, before buying a new one and installing it?

When I press the microswitch a pump starts up and water flows .

(It model number 40003916 )

Thanks in advance,

Danny

 

[Gasguru]

Is the pipework from the boiler, around the pump and motorised valves secured clipped? Does the system have an automatic bypass valve between flow and return before the motorised valves? (as it should do)

As the valve shuts off (when the cylinder hot water is up to temperature) the water inertia can cause a bang as the flow is suddenly stopped through the valve. If there is no bypass or it is (incorrectly adjusted) this may cause it. I have seen this problem before on a customers new system but we never really got to the root of the problem (I think it was due to poor clipping in ductwork no longer accessible).

Try turning the cylinder thermostat up and down to allow the valve to operate and see if it coincides with the noise.

 

[meldrew's_mate]

Firstly eliminate the boiler. Isolate the gas by turning off at the meter, the Suprima drives the pump from it's PCB so it must be left on. Does the bang occur now on system start-up? Does it bang every time the system starts, coinciding with programmer timings? Does it bang shortly after turning-up the Megaflow 'stat?

Have you a two port valve feeding the cylinder? Is it, maybe, a combination of 3-port and two port valves? Is the 3-port valve free to move, and does it return smartly when the lever is released?

Have you a by-pass valve, manual or automatic? Does it bang when the by-pass is fully open, or the auto by-pass set to a very low level?

Is your pump old? Does it still bang with the pump set to maximum speed?


So many questions, all relevant to your diagnostic needs. Work through methodically and see if you can identify one thing which is constant to the symptom. As I was once told as a method for fault finding "What is it, and what isn't it"

 

[willidh]

Gasguru,

All the pipework appears to be securely clipped. And yes there is a bypass valve, with a knob - I guess so you can adjust the rate of flow.

Yesterday, I was able to recreate the problem using the cylinder thermostat - when I turn the temperature down, after the water has been flowing for a while, the powerhead releases the valve and the flow of water into the Megaflo stops, causing the bang.

So I opened up the valve a bit and thought that had fixed it. However today I heard another bang.

meldrew's_mate,

The problem is when the boiler turns off, so I don't think it is the boiler - rather it is something happening too quickly - some sort of pressure wave or oscillation.

I believe it is a two-port valve feeding the cylinder. It is a piece of pipe with the powerhead on top. (I guess three-port would be t-shaped, which this is not)

The pump is 5-6 years old. I think it still bangs at maximum speed (it was set to 1 - maximum of 3).

I assume that the bypass valve is adjustable for a reason. What is that reason? What would be the impact if I opened it all the way up?

On the horizontal section of pipe from Primary return of the Megaflo there is a t-shaped piece of pipe, with the "leg" of the T pointing up. It has a knurled cap which unscrews. I presume this is a device for reducing water hammer.

Thanks for your help so far.

Danny

 

[willidh]

I thought i'd bring this topic back to life as I still have the banging noise when the motorised valve closes and am no closer to finding a solution.
Any other ideas?

Danny