Noisy Hot Water - Expansion pipe drawing in water

[Tesla]

Hi all,

I have a Baxi back boiler with hot water cylinder in bedroom and F&E tank in attic. Quite a small system, 4 rads and 1 towel rad.

The heating and hot water system are performing fine, no issues with cold spots and hot water is good.

The issue is a very noisy system. I am regularly able to bleed out a small amount of air from the upstairs rads and/or vertical pipes next to cylinder and pump.

I have observing behaviour of the system and am fairly sure the whooshing noises only occur when the hot water is switched on. Heating only, no noises.

If the hot water is switched on with the heating the sound of air circulating around the upstairs radiators follows this whooshing.

With the system cold I held a pint of water over the expansion pipe up in the attic and had someone switch the hot water on, almost a whole pint was sucked up pretty much straight away. I refilled the glass and held it under the expansion pipe for a further 10 mins but only air was expelled, no more sucking.

Is this normal behaviour? Should the expansion ever suck? I'm thinking not and it's drawing in air causing all of the noises.

I have opened the rad bleed valves with the system running whilst I can hear this air flowing through the rad, particularly noisy at the TRV, but no air comes out of the rad bleed. Why is this? Does the flow of water carry it straight out of the rad?

Thanks a lot for any help and advice.#

EDIT - I should add that the F&E tank doesn't look very dirty, a very thing layer of orange/brown in the bottom. Thickness of paper.

 

[twgas]

Could be several problem(s).
Is the vent pipe high enough?
Is the system piped properly?
Is pump correct, setting & size?

 

[45yearsagasman]

Should the expansion ever suck? I'm thinking not

You are quite correct. This needs to be rectified as it will damage your system if left. This is usually caused by poor system design, or more likely a restriction around the feed and vent connections if your system is fully pumped with a zone valve.

 

[Tesla]

Could be several problem(s).
Is the vent pipe high enough?
Is the system piped properly?
Is pump correct, setting & size?

Thanks for the reply.

I'll post the pump's spec, it's on the slowest setting.
Would a couple of photos of the pipe work be beneficial?

How high should the vent be?

 

[Tesla]

Should the expansion ever suck? I'm thinking not

You are quite correct. This needs to be rectified as it will damage your system if left. This is usually caused by poor system design, or more likely a restriction around the feed and vent connections if your system is fully pumped with a zone valve.

I've just read up on the magnet test so going to try that shortly.

Yes, I believe fully pumped as has a 3-way zone valve. Replaced around 2 years ago.

 

[twgas]

Decent pics are very often a great help
Preferably some fairly close and some not so, as an overall picture needs to be observed.
How high is it? I ask because a lot of people will say" yea, that's what it is"
Saying what someone may want to hear is not usually helpful, truth is best.

 

[Tesla]

Decent pics are very often a great help
Preferably some fairly close and some not so, as an overall picture needs to be observed.
How high is it? I ask because a lot of people will say" yea, that's what it is"
Saying what someone may want to hear is not usually helpful, truth is best.

Thanks again, I really appreciate your assistance.

Sorry to sound a bit dopey, where shall I measure the vent from? The distance from the feed at the bottom of the tank to the expansion pipe fixed over the top?

I'll sort a few pictures out and post them up very shortly. Will snap a few of the attic setup too.

 

[twgas]

Water level to highest point of vent

 

[Tesla]

Punp: Grundfos UPS 15-50
Vent height: 20cm above FE tank water level.

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[Tesla]

Cannot get a magnet to stick to any of the feed pipework.

 

[JohnD]

Vent height: 20cm above FE tank water level.

Is that measured to the top of the bend? the vent should rise (usually vertically) then come back down to the tank in an inverted "U"

20cm is not enough

 

[Tesla]

Vent height: 20cm above FE tank water level.

Is that measured to the top of the bend? the vent should rise (usually vertically) then come back down to the tank in an inverted "U"

20cm is not enough

Hi JohnD,

If you check my last picture above I measured the water level to the copper-coloured section of the vent pipe, this is the highest point of the vent pipe in the entire system.

That is the highest section of vent pipe. It continues horizontally (out of image) for 10-20cm and then right angled downward in to the cupboard in the other photos.

I can take some more pictures if beneficial.

 

[JohnD]

change that for a start then

this is a more typical shape but the top of the "U" should be a couple of feet higher that the waterline (the black hose in the picture is drawn for a different purpose)

 

[Tesla]

Thanks John.

I haven't ever observed water coming out of the expansion.

Quite easy to change so will get this done later today.

Googling suggests going with 450mm above the water line?

 

[JohnD]

450mm is probably OK, but to my mind, if you're going to the trouble of changing it, I like a bit of overkill. Use pipe clips to fix it to the roof timbers to prevent it waving around.

while you're up there, fit Climaflex or similar to all the pipes in the unheated loft. It should be the BS (bylaws) grade which is as thick as your arm.

As you have a vented system, and I see some mud in your F&E tank, it is always worth giving it a clean with Sentinel X400 as you may have sediment interfering with the flow. You'll know it is starting to work when yoyr circulating water goes jet black with loosened sludge. Bale the mud out of the bottom of the tank first and sponge it clan with bleach. Presume you have a close-fitting plastic lid for it? the vent pipe should go through the lid, you can cut a hole or notch with a stanleyknife.

Can you post a pic of the F&E (15mm) pipe, and the Vent (22mm) pipe where they join the circulation pipes, and say how far they are from the pump, and which side of it (the suck side or the blow side, there is a flow arrow cast into the back of the pump)