Banging pipes and the expansion vessel

[espin]

Hello

I'm fairly competent with figuring out most plumbing work in the house, but this has me stumped. My pipes bang a lot... If I open-shut any cold water tap and there's a bong. When the toilets finish filling there's a final bong when the inlet valve close too.

I have a megaflow and it is kept <2bar but regularly drops to 1bar over a couple weeks.. the tundish is always dry.

Thinking that I might have to put in a water hammer arrestor, I thought that I must have an expansion vessel somewhere. I recently discovered it in the loft hidden behind the old disused water tank lying in a tangled mess of pipework on lying on the loft insulation. See attached photos.

I thought that my expansion vessel might be dodgy, but I've given it a good tap and it sounds dull at the water end and hollow at the air end. I gave the Schrader valve a very quick blast and it hissed air, so I think the vessel is fine. It was stamped as manufactured 2006 rated at 4bar.

I can't figure out the pipework though... whether it is in the loop, on a spur and if one of the pipes is a drain for the pressure relief (rated at 3bar).

The gauge here is actually maxxed out. I thought it read 0bar until i realised that the black needle has gone all the way around. Letting the tiny amount of air out of the capillary vent and the gauge did move slightly, so I think that's right.

So many questions....

What the heck is going on with the messy pipework?
Where is the relief valve going to dump out to?
Should that bypass remain closed (as it is) and what is it used for.
Is that pressure reading acceptable? Do I need to bleed something?

(I will find plumber if this starts getting complicated!!)

 

[Harry Bloomfield]

It looks like a DIY job. The fill valves are in your photos, as is a pressure gauge which looks as it is indicating too low a pressure. I'm assuming you have another gauge at a lower level, which due to the head of water will read a bit higher pressure.

Banging pipes when taps are turned off, suggests pipes which are not properly clipped. Creaking pipes as the heating heats up and cools is annoying, but difficult to avoid completely.

 

[ianmcd]

you need to pressurise that, and have to say it is a terrible install

 

[espin]

The previous owners got rid of the open water tank, put in a new boiler and megaflow, so adding the expansion tank in the loft fits that timeline.
It feels like a builder did it rather than a plumber, but i've never had issues with the boiler or megaflow services.
The megaflow downstairs has its own filling loop and gauge reading 1.75bar

I think you misread my initial writeup... the pressure gauge on this expansion vessel is NOT 0bar/empty.... it has gone all the way round to about 4.75bar.
I don't know how the 3bar pressure relief (red cap) hasn't fired. would it end up discharging through that empty port and therefore all over my loft?

There is a PRV on the megaflow inlet which I assumed was first in line, however it does branch and I wonder if the branch goes up to the expansion vessel and thus is reading the mains pressure?

thanks

 

[kidgreen61]

A Megaflow usually doesn't need an expansion vessel, it's integral.
That expansion vessel is for your heating system surely?
It's not designed for potable water.
Methinks you're confusing the two (entirely separate) systems.
The water hammer will be down to an issue with the mains cold system

 

[espin]

I don't know... I will have to quiz my plumber the next time he comes to service the gas boiler.

I was previously told that the mains comes in and branches into a direct downstairs feed (for the kitchen and outside pipe) and the other hits a 3bar PRV before going into the megaflow
Whenever we've had the boiler serviced there's never been any indication from the engineer that it's overpressured on the downstairs feed.

I just can't see how the expansion vessel gauge can be at 4.75bar unless it comes off that first branch, but is that safe? The expansion vessel is rated 4bar and the relief valve attached to it is meant to be 3bar?

 

[Madrab]

I'd recommend you get a someone in that's happy to spend a little time figuring out the setup. The gauge may be broken as the system will not be sitting @ over 4bar otherwise that PRV would be dumping all over the place. The PRV does need terminated outside somewhere.

Usually all that would be in the same space as the HW cylinder and then that PRV is plumbed into the same circuit as the discharge for the unvented into the tundish.

The water hammer may be indicative of mains water pressure that's too high, you may need a Pressure Reducing Valve fitted to the mains inlet. Usually the mains would enter the property on the ground floor and then head up to the unvented with the kitchen fed first. You really need to find your mains stop tap, not the one that isolates the unvented as that won't be the main stop tap.

 

[Dangee]

Fairly competent??
Espin, a little bit of knowledge can be very dangerous.

 

[ianmcd]

The previous owners got rid of the open water tank, put in a new boiler and megaflow, so adding the expansion tank in the loft fits that timeline.

and what is the expansion vessel supposed to be protecting ?

 

[transam]

Any non active dead legs some where ? Pipe just capped off that fed some thing ? Possibly / may be