Noisy Hot Water - Expansion pipe drawing in water

[Agile]

The vent should be the FIRST pipe after ther boiler with the feed within 150 mm afterwards!

The most common problem is pumping over whereas your problem seems to be sucking and makes me wonder if its correctly arranged.

Tony

 

[Tesla]

Thanks again chaps.

Hopefully the attached will help further. I have described my labels in case I have incorrectly labelled.

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• Tesla
• 8 Dec 2012
• 1

Mains water feeds ball cock valves in F&E cistern and DHW attic cistern.
Feed is from pipe in bottom of F&E cistern.
Vent is pipe that hangs over F&E cistern, the one I am to extend.

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• Tesla
• 8 Dec 2012
• 1

I have highlighted pump direction.

This lower section of the feed pipe is also the return from the hot water tank coil.

 

[JohnD]

Aha

It appears that the Vent is attached to the suction side of the pump, is that right?

But the feed appears not to be

That would cause a pressure difference between the two, and the vent pipe to suck air.

It might always have sucked air, or it might have got worse with a bit of sediment or faster pump, or if the pump has been replaced the other way up.

That piping needs to be changed. The feed and the vent should both be on the same side of the pump, and only a few inches apart.

 

[Tesla]

Hi JohnD, thanks again for your time and expertise.

Yes, that's correct.

In the summer I replaced all but one of the rad's and flushed the system through (although didn't mop out the F&E cistern, will do so now) so perhaps this cleaned system has exaggerated the ever present problem? I couldn't bleed the old rads properly as the bleep valves were all rounded off (couldn't replace as the welded in type).

To quote the Baxi manual:

The cold feed pipe (15mm min) should preferably be connected to the boiler return.

Close coupling of the cold feed pipe to the flow pipe at a maximum of 150mm (6 in) from the vent pipe is permissible but there must always be an open cold water path to the boiler return connection.

I don't understand what " there must always be an open cold water path to the boiler return connection" means.

Having studied some diagrams on other sites the follwing doesn't seem quite right. The return from the hot water coil goes into the feed pipe and then into the return to the boiler all in 15mm, as pictured below. Is this OK? I read up on the 3 Tees Rule.

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• Tesla
• 8 Dec 2012
• 1

 

[twgas]

your system is piped wrongly. the feed and vent should be arranged as said earlier. the vent pipe should be AT LEAST 450mm above the water level.
the corrosion on the vent pipe says it pumps over, probably just a slug when system is turned off.
until the pipework is corrected there is little point in doing anything else.

 

[Tesla]

your system is piped wrongly. the feed and vent should be arranged as said earlier. the vent pipe should be AT LEAST 450mm above the water level.
the corrosion on the vent pipe says it pumps over, probably just a slug when system is turned off.
until the pipework is corrected there is little point in doing anything else.

Thanks for the reply.

Did you see my quote above from the Baxi boiler installation manual stating taking the feed in to the return side is preferable?

Am I correct in thinking that the water level in the vent pipe is equal with the F&E cistern level? If so, will extending the vent pipe actually help?

I am not questioning your advice, I like to know how and why things work to understand them better.

I cranked the pump up to fastest speed for about 20mins. The system was very noisy and the F&E cistern water started to get warm. No water came out of the vent pipe though. Air bubbles did come out of the feed.

 

[twgas]

Did you see my quote above from the Baxi boiler installation manual stating taking the feed in to the return side is preferable?.

yes, I'm suspecting your boiler is quite old, before systems were fully pumped the return was usually connected to the return of the cylinder.

Am I correct in thinking that the water level in the vent pipe is equal with the F&E cistern level?.

when system is off, yes.

If so, will extending the vent pipe actually help?.

yes, the initial surge of the pump can push or pull water so the higher the pipe the less chance of it reaching the top.

I am not questioning your advice, I like to know how and why things work to understand them better.

thats ok.

 

[Tesla]

Thanks again, I'll reconfigure the feed pipe and report back.

Any ideas on what " there must always be an open cold water path to the boiler return connection" means.

 

[twgas]

Any ideas on what " there must always be an open cold water path to the boiler return connection" means.

It means, basically, there must be an unrestricted route from the f&e tank to the boiler, some boilers can use the same pipe for feed and the vent.

 

[JohnD]

"unrestricted" mostly means there mustn't be a valve in the way, or anything else that could prevent water or steam escaping, such as a pump.

 

[Tesla]

Thanks yet again.

Just a thought, what height should the F&E tank be at?

Where is this measurement taken from? Highest flow/return pipework in system?

 

[Tesla]

Hi chaps,

Drained the system this morning and cleaned out the F&E cistern. No brown slime any longer!

I backfilled the system and then ran it a bit to get all of the air out.

I then opened up the drain but left the cold water main supply on and just left the system flushing through. No idea if this was worth it. It was recommended to me to tap/lightly hammer the elbow where the feed meets the boiler return with the fresh water running through it as it may dislodge a suspected blockage. As you can see it's quite tight in that cupboard and the install is quite neat and tidy so thought I'd try this before chopping a bit of pipe work out to visually inspect/clean.

The thing that's on my mind is that the F&E cistern emptied quite quickly, placing my finger over the feed hole in the cistern proved there was good suction/vacuum at this pipe too. Would this be the case with a partially blocked feed?

The other thing on my mind is should the F&E tank be raised thus also increasing the water level/volume in the vent pipe. I read that the pump will suck on the vent a little when first kicking in until the system balances. Perhaps there is not enough water in the vent pipe to allow for this initial suck? Or am I talking rubbish?

My mornings fiddling/flushing doesn't appear to of helped. Still get a whoosh through the pump followed my air bubbles flowing through the two upstairs bedroom rads, oddly the upstairs bathroom towel rad never seems to have any air in.

 

[Agile]

If the F&E is emptying quickly then the feed pipe is not blocked.

The vent pipe must be correctly connected and at least 450 mm above the level in the tank.

Tony

 

[Tesla]

Thanks for the reply.

The vent is less than 450mm but I cannot see how raising it will effect as it's not pumping water out the vent. An easy issue to rectify though.

I am going to cut into the feed above the elbow and rod it through and then flush with cold water draining into a bucket.

I'm not expecting anything but it's another easy thing to tick off the potentials list.

 

[JohnD]

you need to start by moving the Vent pipe connection from the suction side of the pump and putting it next to the F&E pipe.