Vent pipe pumps over when CH turns off

[Alfie25]

I have a fully pumped open vented system with a 3 port valve. At the point when the pump shuts off after the CH has been on, the system pumps over out of the vent pipe. It's like the sudden stop in flow causes a surge and expels a short burst of water out of the vent pipe. It does not appear to pump over at any other point when the CH is on, just when the pump turns off after the CH has been on. It also doesn't do it when just the HW has been on.

I don't believe there is any blockage in the cold feed from the F/E tank, as the system was drained a few months ago (to replace a couple of radiators) and it filled back up fine.

I'm not sure if the system has always behaved this way or not, as I moved into the house just a few months ago. Can anyone please advise on what could be causing it, and the consequences of the problem.

 

[ianmcd]

what boiler do you have Alfie ? and yes this will corrode the system internally as your F&E tank will constantly be making up the lost system water that is being lost via the expansion pipe

 

[Alfie25]

It's a Worcester Greenstar 12 Ri. On a side note, it fires up by itself for about 2 minutes at what seem like random intervals (maybe once/twice a day). When I say by itself, I mean both CH and HW on the main control is set to Off. Can't be some frost protection feature as we're in summer! Is it normal?

 

[Nige F]

what boiler do you have Alfie ? and yes this will corrode the system internally as your F&E tank will constantly be making up the lost system water that is being lost via the expansion pipe

Where`s the water being lost to - try turning the pump speed down

 

[Alfie25]

It was on speed 3 when I moved in (and rather noisy). I've got it on 2 now which is adequate and less noisy. Speed 1 isn't enough.

Nige F - the water is actually is being lost, because the vent pipe is over the big cold water tank, not the F/E tank. No idea why it's been set up this way.

 

[Agile]

Its not! He is wrong! Thats the problem of DIYers trying to give advice!

But it does oxygenate the pumping over water which then rusts the inside of the rads and will cause sludge and pin holes soon!

Its almost certain to be a wrong or blocked pipe where the vent joins the system and some air somewhere. Try bleeding each rad with system off.

Tony

 

[Alfie25]

Its not! He is wrong! Thats the problem of DIYers trying to give advice!

But it does oxygenate the pumping over water which then rusts the inside of the rads and will cause sludge and pin holes soon!

Its almost certain to be a wrong or blocked pipe where the vent joins the system and some air somewhere. Try bleeding each rad with system off.

Tony

It's not what? I only have 1 vent pipe and it's over the cold water tank. No vent over the f/e tank so does this mean I have a combined feed and vent pipe of the f/e tank?
I've bled the rads several times with the system off (but still warm) but I keep getting air in the system and I can't figure out where it's coming from.

Can the pump generate air? I've bled it several times and only a split second 'phuttt' of air comes out, but when running it's constantly making a noise like it has air in it. It builds up as the heat increases and sounds like it's boiling and releasing little bubbles.

 

[HERTS P&D]

Tony did you call Nige a DIYER?

I wish I knew half as much as Nige.



Andy

 

[Nige F]

I had an apprentice once , I taught him all I know - and he still knows nowt He B.S `s his way around to this day . Lying - like a badly fitted carpet . He`d take a measurement and it`d end up 3 mm short - He`d say " there`s nothing in it " Like my front room . His level had a fixed bubble . If I knew half of what Agile knows about electronics - I wouldn`t have been a plumber , that`s for sure

 

[doitall]

Its not! He is wrong! Thats the problem of DIYers trying to give advice!

But it does oxygenate the pumping over water which then rusts the inside of the rads and will cause sludge and pin holes soon!

Its almost certain to be a wrong or blocked pipe where the vent joins the system and some air somewhere. Try bleeding each rad with system off.

Tony

One should assume the system has an inhibitor to prevent that Tony.

The problem is the head is not high enough, raise the header tank and the vent pipe.

At the same time stick it over the right tank, if it's the heating pipe that.s surging over.

How many vent pipes does the storage tank have over the top.

 

[Whitespirit66]

Am I missing something? If the OP says his system is pumping over from the vent pipe, but it's the vent pipe over the CWS as he has no vent over the F&E, then it's coming from the hw cylinder. Not the ch system.

 

[doitall]

That was my concern Whitespirit and why the questions.

 

[Agile]

I was refering to ianmcd. He wrongly at the time said water would be lost and made up.

But we now know that there seems to be a further problem if the vent is over the wrong tank. If that is so then the F&E will be refilling to make up the lst water.

Most systems dont have any inhibitor. In any case inhibitor cannot prevent rusting of rads caused by oxygenation from pumping over or regular refilling.

The heating system cannot cause water to vent from the HW cylinder vent as there is no connection ( unless a primatic cylinder ).

But if there is an F&E tank then its not a primatic!

Tony

 

[joe-90]

Yay! Tony kicks ass.

 

[doitall]

The heating system cannot cause water to vent from the HW cylinder vent as there is no connection ( unless a primatic cylinder ).

But if there is an F&E tank then its not a primatic!

Tony

But it's most unusual to find a htg vent pipe over a storage tank, quite apart from the danger to the occupants from contamination.