Groaning from hot water taps in pressurised system

crazy600

Has anyone any ideas?
I have this loud groaning noise coming from the area of my pressurised hot water cyliinder, which includes expansion vessel.
I had this problem a while after this new system was put in, had many plumbers look at it, and there only sugestion was to move the grunfos mq pump to the ground floor(it was orig in attic with cylinder) and turn expansion vessel on its side.
Did this, with much expense and hey presto problem gone! now 6months later the noise is back again (it would wake the dead). help please:(

Have the expansion vessel charge checked so that it matches in coming mains/pumped pressure, have the expansion vessel as near to the cylinder as possible and try to make sure there is little or no air on water side of expansion vessel, if you bang it you can hear if it's empty, if you only have the hot on the pressure reducing valve then it's possible to over pressurize via any mixing taps(less likely if pump is under 3 1/2bar), check the combination valve for any grit, check temperature controls and any motorized valves for correct operation, Gary.

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crazy600 wrote: »

Has anyone any ideas?
I have this loud groaning noise coming from the area of my pressurised hot water cyliinder, which includes expansion vessel.
I had this problem a while after this new system was put in, had many plumbers look at it, and there only sugestion was to move the grunfos mq pump to the ground floor(it was orig in attic with cylinder) and turn expansion vessel on its side.
Did this, with much expense and hey presto problem gone! now 6months later the noise is back again (it would wake the dead). help please:(

Gary has given some good info, hard to tell for sure unless you can pin point the area of noise. When installing pressurized systems installer has to have head screwed on. Everything after MQ pump has to be regulated to suit high pressure from pump and then the extra pressure created from hot water expansion.

I noticed a similar problem with a pressurized system, on cold feed to cylinder the plumber who made up connection to cylinder thread used too much flax, a build up of flax restricted the opening into cylinder. Pressurized water rushed passed flax giving a vibrating / groaning type sound each time cylinder required filling. Took a bit of head scratching to find it in the end.

When do you hear sound, after a shower / bath? after cylinder recovers (heats up)? All the time?

Might not even be cylinder related depending on what other pipes are close by.

More info might lead you to the solution.

crazy600

It sounds like gary71 might be on the right track.
I checked the pressure on the feed going to the cylinder (potable expansion vessel), it's pressure was 3.0bar and it should be pressurised to 3.5, the mq pump is a 4 bar. There is also a smaller expansion vessel(8ltrs) on hot water flow from cylinder (cylinder is 250ltrs) is should be pressurised to 1.5bar at it's reading .90bar.
The system was underpressure when I took the reading, as i dont now it I need to check it with or without pump pressure on.
I dont have any motorised valves, i have a system link unit with small pumps for every zone on the heating system:o

You would need to turn off the pumped supply to the cylinder, open the hot tap to release pressure, then take a reading of the pressure in the expansion vessel from the test point on top, it should match the incoming pressure what ever it is, as you have a 4 bar pump i would be tempted to fit a adjustable pressure reducing valve on the cold after the pump before it branches off so you can play around with the pressure to see what impact it would have by lowering it, the hot and cold water pressure needs to be the same across the installation or you can have noise issues, also try turning down the cylinder stat, if the problem is heat orientated then it would point toward a pressure issue, the hotter the cylinder is the higher the pressure in the cylinder, Gary.

crazy600

Thanks Gary, tried that and the pressure on the hot water side is very low only .85bar, if i turn down the pressure on the mq I don't have enough pressure in the attic ensuite, i think the q might be lowered to 3.5bar, when system was repressurised i think the hot h2o expansion vessel was vibrating, as i just about made it to the cylinder room when i turned back on hot tap (hard to say exactly, its a two man job).
Could the vessel be too small for the job? the cold water vessel is supposed to be pressurised to 3.5bar but it only read 2.75 and its alot larger in capicity anyway.
The cyslinder stat is set at 55degrees

The pressure on your heating circuit wouldn't be a issue, lowering the temperature of the cylinder stat would be for a test only to help identify if the problem is effected by pressure, i would advise you to turn your cylinder stat to 60c to help prevent any issues with legionaries, sometimes cylinder stats can be out so if you turn it up and things are to hot see what the true temperature is at the tap with a thermometer.

Back to your noise issue, the biggest problem is with copper pipes the noise resonates making it difficult to pin point the cause. Normally i find noise issues are to do with the positioning of the cylinder expansion vessel, air in the expansion vessel on the water side, the air is held under pressure and when the taps opens it creates a noise as it races out only to be forced up into the expansion vessel again when the tap is closed, this normally occurs when the cylinder has been sitting a while and the pressure has built up. If the pressure in the expansion vessel doesn't match the incoming pressure then when the cylinder is left to cook for a while the increase in pressure on the cylinder side can cause the non return valve in the combination kit to vibrate as it bangs shut until the pressure equalizes, also check the combination valve they tend to have filters and a buid up of dirt can cause problems. In a few cases taps have been the cause, you can try opening the temperature/pressure relief valve on the cylinder when you want to test, save you having to open a tap.

One other thing as you don't have a motorized valve it is possible to over cook the cylinder increasing the pressure in the cylinder, you can test this by using your immersion instead off the boiler to heat the cylinder for a day or two as a test, Gary.