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hi all, i have recently had a new combi boiler fitted and since then i am plagued with water hammer. i have researched this and some fitters are saying it could possibly be caused by the stop cocks i fitted to isolate various parts of the house and extension. i have read that fitting check valves could eliminate the water hammer. has anyone else tried this and with what success or dissapointment? i know this seems to be a common fault on new properties but my house is some 60 odd years old and this only started after the new boiler and stop cocks were fitted. thanks for any help provided, stanman
 
Is it on the hot circuit ? The water hammer

If so needs a shock arrestor fitting on the cold supply to the boiler
 
Is it on the hot circuit ? The water hammer

If so needs a shock arrestor fitting on the cold supply to the boiler
its on both hot and cold, and whenever anyone in my terrace uses any tap, washer toilet etc i get the knock as whatever appliance fills and shuts off. thats why its so annoying
 
hi all, i have recently had a new combi boiler fitted and since then i am plagued with water hammer.

What type of system did you have before?

There are several types of water hammer. Most likely candidates in your case are:

1. Due to a combination of turbulent flow occuring somewhere and incorrectly secured pipes. All is fine if you open a tap gradually but as the flow rate increases the hammering starts and builds up.

2. Another occurs when there is a sudden change in flow rate when a valve is shut suddenly.

Do either of these descriptions match your problem? I'm talking about a repetitive banging, not a single 'clunk'.

First thing to check is the same in all cases (including a single 'clunk'), i.e. that pipe runs are properly secured. I don't have the BS to hand but from memory, horizontal 15 mm waterpipes should be clipped to a solid support at centres that at most 1.2 m apart. I don't like anything more than 1 m myself. Second thing to check is the supply pressure is within correct limits. If both these are okay you are looking at resizing pipework, changing valves, or fitting surge arrestors
 
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its on both hot and cold, and whenever anyone in my terrace uses any tap, washer toilet etc i get the knock as whatever appliance fills and shuts off. thats why its so annoying

Did the combi-installers increase the diameter of your incoming supply pipe, by any chance?
 
A shock arrester close to the boiler will fix it.
Some boiler manufacturers specify one in the install guide.
 
What type of system did you have before?

There are several types of water hammer. Most likely candidates in your case are:

1. Due to a combination of turbulent flow occuring somewhere and incorrectly secured pipes. All is fine if you open a tap gradually but as the flow rate increases the hammering starts and builds up.

2. Another occurs when there is a sudden change in flow rate when a valve is shut suddenly.

Do either of these descriptions match your problem? I'm talking about a repetitive banging, not a single 'clunk'.

First thing to check is the same in all cases (including a single 'clunk'), i.e. that pipe runs are properly secured. I don't have the BS to hand but from memory, horizontal 15 mm waterpipes should be clipped to a solid support at centres that at most 1.2 m apart. I don't like anything more than 1 m myself. Second thing to check is the supply pressure is within correct limits. If both these are okay you are looking at resizing pipework, changing valves, or fitting surge arrestors
i had a combi system before. i had to have the boiler resited and as my previous boiler was 9 years old i thought i would kill two birds with one stone. the earlier boiler was a glowworm beta 30! this boiler is the latest glowworm 30! although the fitter said it is virtually a new vailiant other than the name! i just cant under stand what could possibly be so different in the systems to cause all this noise. (it is a single knock by the way} but it is a strong knock and has at times woken me in the morning as the neighbours get up and start using their facilities. toilets, etc. washing machines and dishwashers are the worst because they stop, start, stop, start, then i get the knock each time. the pipes are clipped as per instructions sometimes even more than advised! the only difference is the boiler and two extra stop cocks as i said earlier, feeding different parts of the house! i have read on here the knock valves dont always work that is why i was asking if changed the stop cocks for check valves if that would cure it?
 
i had a combi system before. i had to have the boiler resited and as my previous boiler was 9 years old i thought i would kill two birds with one stone. the earlier boiler was a glowworm beta 30! this boiler is the latest glowworm 30! although the fitter said it is virtually a new vailiant other than the name! i just cant under stand what could possibly be so different in the systems to cause all this noise. (it is a single knock by the way} but it is a strong knock and has at times woken me in the morning as the neighbours get up and start using their facilities. toilets, etc. washing machines and dishwashers are the worst because they stop, start, stop, start, then i get the knock each time. the pipes are clipped as per instructions sometimes even more than advised! the only difference is the boiler and two extra stop cocks as i said earlier, feeding different parts of the house! i have read on here the knock valves dont always work that is why i was asking if changed the stop cocks for check valves if that would cure it?

Check valves are primarily designed to prevent reverse flow but as a side-effect of the way they work (typically a ball and spring arranged to allow one-way flow) one on your incoming feedback may be enough to block the shock wave that is coming in from your neighbours. Personally I'd go for a purpose-designed surge arrestor or expansion tank. Really it's your neighbour(s) that should have the check valve(s) as they're the ones pumping water back into the main!

It's possible that your original system, by accident or design, had a vertical stub that contained air and that acted as a surge arrestor. If this was removed in the re-siting process that could explain why the hammer suddenly became a problem at the same time as the new boiler was installed.
 
thanks Chuck, i already have a 12 litre expansion vessel fitted to the pipe work on an Ariston electric water heater. would this not absorb the incoming shocks? it is fitted in my extension but it is all on the same system
 
thanks Chuck, i already have a 12 litre expansion vessel fitted to the pipe work on an Ariston electric water heater. would this not absorb the incoming shocks? it is fitted in my extension but it is all on the same system
You will still need a shock arrester on the incoming main to the boiler
 
thanks Chuck, i already have a 12 litre expansion vessel fitted to the pipe work on an Ariston electric water heater. would this not absorb the incoming shocks? it is fitted in my extension but it is all on the same system

From your description, it's in the wrong part of the system to be effective. You need an arrestor as close to the incoming 'main' as possible, immediately after your stop-cock will be best.

I'd still get the water pressure checked.

C.
 
From your description, it's in the wrong part of the system to be effective. You need an arrestor as close to the incoming 'main' as possible, immediately after your stop-cock will be best.

I'd still get the water pressure checked.

C.
sorry , that is, what i meant, i didnt explain properly, thanks chuck
 
ive just fitted a double check valve immediately after the stopcock and it has cured the problem!! i had a water hammer arrestor ready to fit but thought i would just test the CV theory out first. I'm just waiting till some neighbours get in and start using their facillities to be 100% sure! it has definitely stopped the knocking in my house and the extension. i am so pleased!! i will get back and let you know what happens, cheers, stanman
 
ive just fitted a double check valve immediately after the stopcock and it has cured the problem!! i had a water hammer arrestor ready to fit but thought i would just test the CV theory out first. I'm just waiting till some neighbours get in and start using their facillities to be 100% sure! it has definitely stopped the knocking in my house and the extension. i am so pleased!! i will get back and let you know what happens, cheers, stanman
All good ,i'm pleased to say ! No knocks or bangs no matter what anyone uses.
Just like to say thanks to anyone who offered suggestions. No doubt i will be back to pick the brains of others in the future. Stanman
 
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