Pumping over problem

[beermatt3]

I have been called in to a job to look at a heating system that has a serious pumping over problem. It is a two story house with boiler on ground floor, pump and three way valve in airing cupboard on first floor. The cold feed and vent tee into the common flow in airing cupboard. (seperatly both 22mm)

The system has been flushed and shows no signs of any blockages, but as soon as the pump goes on in either heating or hot water it shoots out the 22mm vent pipe even when cold.

I reckon I have been called in to sort a problem that never has been right since installation as the water in expansion tank was very brown.

Any suggestions, I no it's the weekend but I would be gratefull for any comments.

Will making the expansion pipe higher make any difference?

[ollski]

What speed is the pump on?, is the open vent the next connection after the pump?

[andsam]

As Ollski says tell us more about the pipework config.
1 Where the open vent is
2 Where cold feed is
3 Are they positioned before the pump.
3 How far are these apart
4 How high does the open vent go above the header tank.

[beermatt3]

1 Where the open vent is
2 Where cold feed is
3 Are they positioned before the pump.
3 How far are these apart
4 How high does the open vent go above the header tank.

Thanks for quick response.

The cold feed and open vent are positioned on a piece of verital pipe about 2" below before the the pump and about 2" apart.

The vent pipe goes about 4" above the header tank.

I hope this is of use!

[beermatt3]

It doesn't make any difference what speed the pump is on, even on 1 it still pumps over.

What a nightmare, who would be a plumber!

[PIPERPETE]

If youre having pump back then the expansion pipe is fitted after the pump and not before, also the motorised valve could be closed, i suspect a wiring problem that the motorised valve has not been wired to switch the boiler and pump off, another prblem could be is it an old house? if it is then at some time the system would have been on gravity central heating and gravity hot water and there could be a non return valve jammed in teh flow pipe somewhere. Thinsk about it, if you are confused then draw a diagram on paper then have a cup of tea, trust your instincts

[beermatt3]

The pump and motorised valve are new, so I don't reckon they could be at fault. All the rads and cylinder get hot so can't be a circulation problem.

Most odd.

[ollski]

beermatt3 wrote:

The pump and motorised valve are new, so I don't reckon they could be at fault. All the rads and cylinder get hot so can't be a circulation problem. Most odd.

When you say the pump is new are you sure it is fitted the right way round

[beermatt3]

Yep the pump is the right way around.

[ollski]

Try extending the vent pipe, should be 18" above the tank, or combine the cold feed and vent (min.22mm).

[kaboom]

What timing! I flushed one today that had ground to a halt due to very serious sludge. Got it all clean, 3 port ok, fitted shiny new pump and the b*****r pumps over a little on 2. On 1 it won't circulate. The set up is boiler on ground floor and the rest in airing cupboard. Its what I call an 'H' set up, with the feed coming up from the bottom right and turns left (vent is straight up) turns left again (with feed coming down from top left) into pump which faces down. The header tank is sitting on the loft floor and the vent only goes 300mm above it at highest point. Think I'll try raising the header off the loft floor and extend the vent a bit higher too. Any other ideas (other than sealed system) chaps? 14 rad system all bar 1 on trv's, no room stat and manual bypass (which I don't really want to cheat with).

[Softus]

beermatt3 wrote:

The system has been flushed and shows no signs of any blockages... ...the water in expansion tank was very brown.

These two statements conflict. If the system was clean then the water would not be brown.

Water running out of the vent is not the way it's designed to be, so it's a symptom of problem, rather than a problem per se.

One common point of a blockage is at the junction of the cold feed into the pumped circuit. This can be exacerbated by incorrect installation - in the direction of flow, the sequence should be vent, cold feed, pump. If the vent is after the cold vent then there's a risk of pulling in air, and if the vent is after the pump then there's a risk of "pumping over".

The chances are that you're at the beginning of a medium length road leading from an unhealthy system to a healthy one. You may wish to consider the virtues of leaving the work until the spring, but you can mitigate the problem in the meantime.

However, if your system is pumping over, then you may get away with just cleaning it for now. I would do this by draining the water out of the system (with the boiler and pump turned off) until the F&E cistern is empty, then drain the same amount again, then add a cleaner to the cistern and re-fill. You'll need to shut off the cold feed to the F&E while doing this - tying up the ball valve will do if you have no service valve ro stop cock.

Run the system for a couple of weeks in this state - ensure that each radiator gets nice and hot for some of that time. When you drain down after all of this (do it HOT) then the water should contain much of the muck that's blocking your system. You can then add an inhibitor, and refill, and wait until the spring.

BTW, the forum contains information about about blockages, and sludge, and draining, and inhibitors, and pumping over, and blockages, and sludge....

[ollski]

Softus wrote:

However, if your system is pumping over, then you may get away with just cleaning it for now. I would do this by draining the water out of the system (with the boiler and pump turned off) until the F&E cistern is empty, then drain the same amount again, then add a cleaner to the cistern and re-fill. You'll need to shut off the cold feed to the F&E while doing this - tying up the ball valve will do if you have no service valve ro stop cock.

I think personally if I suspected the cold feed to be virtually blocked that I would isolate a rad, drain a couple of litres out of it and inject the cleaner into the rad via the bleed plug....just in case.

[beermatt3]

Thanks everyone, I've got plenty of things to check and try on Monday. When I say the water was brown it is in the past tense, obioulsy it's not brown after being flushed.

Anyway Cheers

[Softus]

ollski, IMO, if the blockage is in the usual place then the cleaner is unlikely to shift it.