Water hammer / noise on hot water system fill

29 Dec 2018
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Pontypridd, Wales
United Kingdom
I previously posted that I thought I was getting water hammer when the header tank in the loft was being filled. I suggested I replaced the float in the tank but the problem did not go away. A plumber suggested that I install a shock arrestor which I did to the pipe which feeds the tank directly. That was installed yesterday but... The noise is still there.

I also fitted some Munsen clips to the pipe to make sure it didn't rattle too much so I don't actually know how much difference the shock arrestor has made. Initially it was much quieter, almost silent where previously the noise would start immediately.

What I have noticed is that the noise and the vibration seems to be coming from below. And also there is a significant amount of gurgling coming from the pipes around the hot water cylinder. The cold water feed goes into a tee with one pipe heading to the loft and the other heading to the boiler system. I haven't traced exactly how it all fits together.

Before I do something daft like fit another shock arrestor on the tea that feeds the hot water cylinder, is it possible that this is something else?
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OK - some clarity. There are two feeder tanks in the loft, the one I changed with a new ball valve, and another which looks much older (covered in cobwebs) but still appears to work. It is covered with an insulation cover. I cannot figure out where it goes to but it is the one that is making noise. Is there ever any need for two black header tanks in the loft? We have an old tin one that had long been disconnected but I wonder if the older one is a remnant of a previous central heating system? Funnily enough, when we moved in, up the loft there was a step ladder in front of it as it about 5 feet up and I can only see into it from a raised view.

It has its own tap - what's the potential harm if I switch off the tap at the tank?
Quick test and this tank is being used. I switched off the tap and lo and hold no noise. I had a hunch about draining off all the gunk from the magna clean and found it consistently dirty. I connected a hose and drained until it was dry. Turning the cold water feed produced no noise. I then went back up with a step ladder and the black at the bottom of that photo is nothing but gunk. A quick refill from the tap itself at the tank indicated that the heating system was filling up. One tank but be filling the hot water and the others the heating.

New tank time! This one with a bloody cover on it to stop that crap getting in there.
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Thanks @denso13. The malfunctioning one looks small though - I read there are regs to suggest it has to be a certain size? Also this thing is mounted on brackets to the wall. Can i replace like with like or is this a bigger job?
bale out the dirty tank into a bucket and sponge it clean. Don't allow the accumulated sludge to run down into your pipework and boiler. If there is any sign of fungal growth or bacterial slime, sponge the tank, lid and ballcock with bleach after cleaning it and before refilling, and let it dry. Don't pour it into the water.

Measure your tank and there is a fair chance that an off-the-shelf plastic lid will fit. You can trim it to fit, and around the vent pipe, with a breadknife or fine saw. Don't do it over the tank as the shavings and particles will fall in the water.

After doing that (and perhaps fitting a new tank with cover) you can use a chemical cleaner such as X400 to loosen the accumulated sludge and sediment in the pipes and boiler, which you will then drain out and rinse, before refilling with an inhibitor to reduce future corrosion. It is easy DIY work if you can get in the loft and can find the drain cock at the bottom of your pipework.

Fit an insulation jacket around both tanks, and plastic foam pipe lagging round all the pipes. Exposed pipes will freeze very quickly in a cold loft. Tanks take a long time to freeze, but the insulation prevents them getting warm in summer which promotes bacterial and fungal growth.

It would be a good idea to lag the pipes this week.
Thank you. The irony is that I have had X400 in the system for the last 2 weeks to lift all the crap and it turns out it was being fed it! I have a rad filled with X100 raring to go although the valves are shut off. Unfortunately, I have about 3 main drain points in the house so draining the system is actually fairly time-consuming. I need to invest in some proper hose to make the job easier. More x400 from Screwfix it is!!!
New ball valve in:

Silent as the grave on filling! No more banging.

Makeshift cover! Best I could do - but this is double sided stuff and I taped down the edges. The insulation jacket went over the top but the damned gunk that came out of it was horrible.
New ball valve in:

Silent as the grave on filling! No more banging.

Makeshift cover! Best I could do - but this is double sided stuff and I taped down the edges. The insulation jacket went over the top but the damned gunk that came out of it was horrible.
that is fine, the lid is simply to stop condensation , and/or debris getting into the tank

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