Pump over question

[John]

By all means point me at a good FAQ rather than answer the question!

The central heating pump is in the first floor airing cupboard. Pipework is generally 22mm.

Feed arrives and then enters a T with straight going into 15mm to the expansion pipe. Right goes about 4 inches to another T where straight is to the pump and the entering pipe is from the header tank (in 22mm). After the pump there is the motorised valve.

The expansion pipe goes up about 1.5m and then there is a "trombone" tube of about 1m before it drops back into the header tank. The header is probably only about 1.2m above top of hot water tank.

Of late it has started pumping over badly - the pump is set to the lowest speed.

Any suggestions why and, more importantly, how to cure it.

Thanks

[Davey]

Blockage or general build up of silt/crap in your system creating greater resistance which ends up with pump-over.

[Dave Plowman (News)]

Assuming the pump speed is switching correctly, is there a bypass loop? This is effectively additional pipework across the pump and sometimes has a gate valve to set the degree of resistance in it. If not might be worth adding one. The simplest way is usually between feed and expansion pipes.

[Davey]

Would that not simply be sidestepping a potential problem? The statement "Of late it has started pumping over badly" is the one to note. Something has happened *of late*, is causing the system to pump over.

[John]

In article , John writes

Just realised I got the order of the two pipes wrong - the feed pipe is the first one and the expansion the second.

[John Rumm]

What sort of layout of vavles has it got? (i.e. Y Plan, S Plan etc):

[John]

[YAPH]

Is the vent pipe a good distance above the top of the water in the header tank? I've seen systems where the vent pipe hasn't been correctly supported and has slipped down so that its open end is near the water level and the system has been pumping over. Raising it again has fixed it. If the water level in the tank is higher than it should be (e.g. due to a duff float valve) that can have the same effect.

[David Hansen]

On Sat, 31 Oct 2009 11:22:00 +0000 someone who may be John wrote this:-

Errr, the feed and expansion pipe is one pipe. When filling "new" water is fed down it to the system. When operating; as the system heats water expands up the f&e pipe into the storage tank, as the system cools water flows back down the f&e pipe.

The other pipe is the vent pipe, which is for safety.

[John]

In article , David Hansen writes

OK - so the first pipe is the feed/expansion and the second is the vent pipe. My question is why does the system suck water down the feed pipe and then squirt it our the vent pipe into the header tank and how do I stop it!

[David Hansen]

On Sun, 1 Nov 2009 15:06:54 +0000 someone who may be John wrote this:-

Suggestions for both questions have already been made.

However, if I understand the description this is the situation

F & E Vent 15mm 22mm | | | | | | | | From boiler -----------------------Pump-----Motorised valve

With pipes splitting "to the right of" the motorised valve for heating and hot water, combining as they return to the boiler? Except for the F&E pipe the pipes on the diagram above are 22mm? The pump pumps water towards the motorised valve?

The sucking water down the F&E pipe is not something I have seen in the description before.

If that is not right please draw it so we can have more of an idea what you are talking about. I doubt if any of us are remote viewers.

[John]

In article , David Hansen writes

/-------\ | | \ |_____| | |

22mm 15mm

|---->------->---Pump-----Motorised valve | From boiler -->-----

Updated your drawing to show what it looks like - with the tank added in and the vent pipe into it.

[David Hansen]

On Sun, 1 Nov 2009 18:57:27 +0000 someone who may be John wrote this:-

Position X Y

Then the vent pipe is too small. It should be 22mm. The feed & expansion pipe could be 15mm, though there is no harm in it being

22mm.

With the drawing as it now is a blockage between the connections of the F&E and vent pipe to the main circuit, position X, would cause water to be pumped up the F&E pipe, for a short period until the pump ran dry. A partial blockage between the vent pipe connection and the pump, position Y, is a possibility.

[John]

In article , David Hansen writes

Sorry - my use of terminology seems to have confused you - it is the vent pipe which is filling the header tank with hot water. So I assume it is sucking water out of the header tank down the F&E and then some is going back up the vent.

[David Hansen]

On Sun, 1 Nov 2009 20:21:56 +0000 someone who may be John wrote this:-

I only put in position X to illustrate a possibility. I didn't think it applied in your case, but it might apply in other cases. Position Y is a possibility though.

[Bob Eager]

Or the heating coil in the HW cylinder has a hole in it....

[Dave Liquorice]

So if I read that right we have:

from boiler --- T1 --- 4" --- T2 --- pump --- valve

The main run from boiler to pump is in 22mm. The branch from T1 is in 15mm and is the vent pipe. The branch from T2 is in 22mm and is the feed/expansion pipe. The gap between T1 and T2 is about 4".

This isn't quite the same as what has been described in your other posts. The size/function is the same but the order is different. ie T1 is the feed/expansion in 22mm in other posts.

How far above the water level in the header tank is the lowest part of that "trombone" bend?

How hard is your water? It's not unknown for there to be a build up of lime scale where the feed joins the main primary pipework. If T2 is the feed/expansion a restriction there will cause there to be increased pressure at T1 and thus more likely to pump over.

[John]

I will go and have another look in the airing cupboard and the loft and double check everything - then post a (hopefully) clearer statement.

Many thanks to you all for the help and advice.

[Doctor Drivel]

The feed and expansion pipes are the wrong way around. The pump should be sucking on the feed pipe first - this should be teh nearest to the pump. The two tees should be next to each other as close as possible. The vent should be 22mm and feed 15mm.

If the boiler has a high limit temperature stat. The existing 15mm vent can be capped off and only the 22mm feed used.