Water discharging from the loft vent pipe as CH turns off?

[Markw996]

Hi,
I have just moved into my first home, a 2 bed semi-detatched and as the title says I have a very noisy central heating system.

As it comes on I get lots of bubbling / gurgling noises that last about 10 seconds and seem to originate from either the upstairs radiators or the airing cupboard.

Also as the central heating clicks off it sounds like someone emptying a bucket of water up in the loft right above my bedroom (very worrying the first time it happened!).
I traced the loft noise to the expansion tank in the loft where, as the heating clicks off, I am getting about half a litre of water discharging from the vent pipe back into the tank.

The system is open vented circa 1992 and I take the vent pipe to be the one that rises about a foot above the tank, then bends in a U shape back down into the tank.

I've had breif discussions with a plumber friend and he says it could be the boiler thermostat?!? but I suspect it is more likely to be air in the system somewhere (although I am certainly not clued up on central heating systems) as I did have to bleed a lot of air from by bathroom radiator when I first moved into the house due to it being very cold at the top.

Just to summarise:
I have 2 tanks in my loft and the problem is relating to the smaller tank which does the central heating.
My boiler is located in a downstairs cupboard.
My airing cupboard is upstairs and contains an immersion tank, pump, and a motorised valve of some sort.

I hope someone can help as the noises wake me up in the mornings and annoy the hell out of me in the evenings! (

Many Thanks,
Mark.

 

[fuzzy]

It is a bypass without a valve. Fitted by an eejit as it is not necessary in the first place and if he fits one, at least valve it.

If the kids don't come through i'll not be doing much tomorrow so i may explain how different systems work with a few drawings.

Clue = neutral point.

yes tamz it is due to the neutral point, obviously punping over is under positive pressure ie, pushing not pulling, did they suss out the problem? is the pump on the right way? if it was working properly then started to fault there must be a reason. if its been like that from new or since some work was carried out then all fingers point to that!

 

[fuzzy]

just read some posts, yes i agree the layout is VIP and therefore as good as it gets, cold feed is the neutral point and therefore the vent is within the neutral zone and shouldnt pump over all else being correctr. ive seen loads of these blocked at the cold feed.

When waters hot it should expand up the cold feed, if it blocks it wont be able to expand into the F&E cistern and has to expand up the vent. then it cannot come back into the system. its not really pumping over as such but expanding over. saying its pumping over leads people to believe theres a feed and vent fault, without seeing the system in operation its hard to say but i agree cut out the tee and replace would be first check.

fuzz

 

[Bartdude]

What's going on?? What's this ancient system? They don't show this on the course.

I'll tell you what,let's rip it out and stick a combi in

 

[tamz]

The basic principles of system design are being lost due to combi's and sealed systems being more popular bit it should be important to know the basics.
There are dozens of ways to pipe a system all based on a few basic layouts.
Understanding how the position of the feed vent and pump effects the water circulation helps.
Here are a couple of drawings. (this could have been a far longer post but i have simplified a lot of things)

I'll start with this one. Basic common layout for a gravity HW, pumped heating on an old cast iron boiler.



The position of the feed connection to the system is called the neutral point. Everything from the pump to the feed is under positive pressure (from the pump) and everything after the feed is negative.
In this drawing the only part of the system under positive pressure is from the pump to the boiler (as this is effectively the point the feed connects). The rest of the circuit is under negative pressure (the water is being pulled).
Because the cast iron boiler holds so much water it also acts as a neutraliser and the water flow from the pumped side slows right down so has very little effect on the gravity side.
It used to be though having the pump on the return like above would help the gravity circuit. In reality it didn't have any real effect.
A system laid out like this will not draw air or pump over (unless a blockage is introduced).


Same system with the pump on the flow. The heating circuit is now under positive pressure (being pushed). This is the better pump position as pumps can push better than they pull.

Move on a few years and motorised valves are introduced and systems become fully pumped. Still using high water content cast boilers, so we get something like this.

Feed and expansion still connected to boiler so position of the pump does not cause it to pump over or draw air. Pump on the flow so the system is under positive pressure.


Same thing with pump on the return. System under negative pressure.


If you use a low water content boiler or the feed and expansion are taken from the pipework, where or how they are connected starts creating problems.

Pipe it as above and a suction effect is introduced to the expansion pipe and if the pump is set too high it will draw air. Fitted like this to a low water content boiler where the pump speed usually had to be set high this is why a lot of systems fitted in the 80's/90's are full of sludge.
Easy quick way to over come this was to combine the feed with the expansion like this

This stopped the problem as the pump had to pull water from the F&E tank rather than air. It was not ideal though.

So they developed this system

Provided the feed and expansion tees were kept within 150mm of each other, the pump would have very little effect on the expansion pipe. Go much beyond the 150mm spacing and it will pump over.

There are dozens of variations of these layouts. Just think how the position of the feed and expansion will effect the system or introduce blockages and think what would happen.

A bit quickly explained and i have missed out a lot but the basic principals are shown. Hope this is of some use to someone.

 

[tamz]

What's going on?? What's this ancient system? They don't show this on the course.

I'll tell you what,let's rip it out and stick a combi in

They don't show much on the courses because they probably don't fkn know. Combi is the answer to everything

 

[fuzzy]

yuve too much time on yer hands tamz!!! lol
youve pretty much said what i said but with more background, i agree alot of newbies tend to favour combis as its all they know. i dont think its the tutors who are at fault, lazy and/or semi skilled plumbers are

 

[tamz]

yuve too much time on yer hands tamz!!! lol

I know lol

 

[SafeGasInstall]

" i dont think its the tutors who are at fault, lazy and/or semi skilled plumbers are"

don't think you were born skilled .....every one deserves a chance and every one who wants to become pro will go through anything to become pro !!!

Thank you for your time TOM !!!!

 

[Horse]

Gents,
New to this so please be gentle.

I have tonight noticed a small amount of warm water spurting out of the vent / overflow pipe into the FE tank when the pump turns off, in water or heating position. Not a lot less than half an egg cup. Only noticed when overflow started dripping outside.
Looking at the vent pipe outlet which was under water its been there a while. (Blue colour)
I have just recently removed and refilled a radiator during decorating. About a week ago.
I have some brown sediment in the tank but whole system is only 10 years old.
I have read the thread and the position of the neutral pipework looks about right.
What height should the overflow/vent pipe invert be above the water level in the tank?
Mines about 4-5 inches. I have seen 18 inches quoted elsewhere but the boiler installation manual says nothing.
When the pump runs I can see a gentle wafting backwards and forwards of sediment around the FE tank outlet.

Any help/advice/sympathy would be gratefully received.
Horse

 

[SafeGasInstall]

dear horse,
first you need some one to see it or picture would help . you have corrosion starting in your system (luck of having inhibitor) ! have you had any air in your radiators lately any cold spots ?

 

[apple-plumbing]

If the Vent pipe is discharging back into the F&E Tank but the water level doesn't rise high enough to reach the Warning Pipe and discharge outside then the Cold Feed from the F&E to the Hot Water Cylinder won't be blocked. The water level in the F&E should be 1/3 full when cold to allow for expansion when everything gets hot. The level should however be above the Cold Feed. The arm of the Ball Valve can be bent down to achieve this. The Cold Feed and Vent Pipe should be as close together behind the CH Pump to encourage Negative Pressure. The boiler could be boiling the water and the Vent doing it's job. The Boiler has a thermostat which can fail and could be checked by a plumber to see if this is funtioning correctly. The Vent Pipe should rise at least 450mm above the F&E and back down in a big arc, to prevent any surge effects - hope this helps

 

[Horse]

dear horse,
first you need some one to see it or picture would help . you have corrosion starting in your system (luck of having inhibitor) ! have you had any air in your radiators lately any cold spots ?

Thanks for the response. I will get some pictures and post. I have no cold spots and the recently removed radiator only had a little black sludge in it. I have had a little air 'single wooshing' in the system recently, twice I have heard it, in the last month. I fitted an auto bleed valve on the radiator in the bathroom (did it as it was a new tall ladder type radiator, over a year ago) I have not had a problem with air in any radiators since. I would add at present the vent pipe outlet is below the overflow level, so when I noticed it today the pipe was 1 inch under water. Have checked the thermostat and it is operating fine. Also it does this in CH a only as well as Hot Water. Again thanks. Horse

 

[apple-plumbing]

If you turn everything off and leave to cool, drain a bucket of water from the CH system via a Drain Valve on the Ground Floor with a Hose, does the level in the F&E drop? This will test for a blockage where the Cold Feed tees into the circuit and the only way expanded water can escape is through the Vent Pipe...this is quite common

 

[Reltub]

Looks from them pics like it's piped up correctly few things i would look at ; Pump the right way round, is there enough head above the pump(2m), flow and returns the right way round.

 

[Horse]

Hi
Thanks for reply the tank did overflow. Well dripped so blocked feed a possibility. As soon as I can( work commitments) I will try your drain refill test and get back. I will change the vent pipe height and arc as well. Thanks for staying with me on this. I will post as soon as I can.
Horse.

 

[tamz]

Raise the vent to around 450 above the F&E and take it out of the water. Bend the ballcock down a bit to reduce the fill level and bail some water from the tank.

 

[SafeGasInstall]

and get some local plumber to power flush you heating and put inhibitor before is to late

 

[Markw996]

Hi,

The plumber let me down on Friday but should be coming Thursday to powerflush my system.
Whilst it's drained I'm going to do a few modifications to the pipework to try to rectify the problems I've been having.

I've finally worked out how to best fit an Aerjec to my system, I'm also going to replace all my leaky or old TRV's, and extend my vent pipe a little bit.

The ballcock has been bent down a bit and I've bailed out about 15 litres from my F&E tank (Feed & Expansion ).

Finally, could someone please give me a BES part number of a good quality bypass valve to fit into my vertical 15mm bypass pipe?

Thanks,
Mark.

 

[fuzzy]

Easiest way to fix - convert to sealed system. The hours spent on determining the problem which may not be easily fixable would best be put to converting it over.

Do not leave it. Every time you draw air in will encourage rapid corrosion of the radiators, or lose water through the overflow will dilute any rust inhibitor.

shouldnt be hard to find, think converting is an expensive cop out

 

[fuzzy]

Hi,

The plumber let me down on Friday but should be coming Thursday to powerflush my system.
Whilst it's drained I'm going to do a few modifications to the pipework to try to rectify the problems I've been having.

I've finally worked out how to best fit an Aerjec to my system, I'm also going to replace all my leaky or old TRV's, and extend my vent pipe a little bit.

The ballcock has been bent down a bit and I've bailed out about 15 litres from my F&E tank (Feed & Expansion ).

Finally, could someone please give me a BES part number of a good quality bypass valve to fit into my vertical 15mm bypass pipe?

Thanks,
Mark.

its a common componentglad your sorting the problem, blocked feed is most probable
just ask at your local plumbing merchant for an auto bi pass,

 

[Bartdude]

I'd use the Honeywell bypass valve on this page.

By-pass, Pressure Reducing Valves & Thermostats<br>Condensate Pump & Fittings

 

[SafeGasInstall]

If it was me i would def change valves before power flush ,but let the plumber do the job other way you might flad the house, and it will be you ho will pay for it !

 

[Reltub]

I wouldn't use an airjec I find the "H" system alot better, also rather than a power flush if the sytem is really badly sludged i would recommend a manual flush i.e taking all the rads off the walls and manually flush outside with a hosepipe, this method is alot better than powerflushing in my opinion and can be quicker and gurantees a clean system, i would then also add some sludge remover to help clear the pipework and give a couple of flushes. Would also repipe the cold feed in 22mm.

 

[fuzzy]

i dont like airjecks, i dont like pumps pointing down either, they recon its fine with an h or airjeck but boisey in my experience

 

[apple-plumbing]

If the conclusion after the 'drain test' is the Cold Feed is not blocked and water is not entering the F&E via a faulty Float Valve (isolate the Float Valve for a few days to test for this), then you may have a breech in the HWSC. The design in 'vented' systems where the CWSC's water level is higher than the F&E means that there need only be a pin hole in the Cylinder's coil for the difference in head pressure between the 2 circuits to force water to backfill into the Primary Circuit causing the F&E level to rise and overflow. The only place these 2 systems mix is in the Cylinder and it's common for an old Cylinder to breech and present you with these symptoms