Pumping over problem

[Ratter]

My CH system is pumping over into the header tank. I have searched through the old posts on the subject and the general wisdom seems to be:-

Top of overflow pipe not high enough above level of water in tank
Corrosion
Too much pump pressure.

I don't think it's corrosion because the house has several zones (some with newish radiators) and all cause the problem

I will obviously be doing what I can with the levels but there's only about another foot of roofspace available. The water level is a bit high so I'll lower that. At the moment there is about 18" of differential - might get it to 3'.

I am suspicious of the pump which is a Grundfos Alpha 15/60 (two years old) - when it was new I seem to remember that wherever you set the adjuster it moved to an equilibrium position whereas now it stays where you put it - can the pressure detector mechaism fail or get blocked by crud - so that it jams on max speed?

Also the overflow pipework is only 15mm - will that make a difference?

Just to add, it didn't do this last year but it is now filling my loft with steam and wife is not happy


All ideas gratefully received.

 

[ChrisR]

None of the above!
Your pipes are partially blocked with scale/crud at the point where the feed joins the system.
A magnet will stick to the pipe because it's an iron complex compound.
Sometimes you can poke a thin drain sping up the pipes, perhaps from the pump side, but often the pipe has to be excised.
The feed can be 15mm, the vent MUST be 22, and the overflow should be 3/4 = 22 ish.

 

[hi-spec plumbing heating]

you say it's not corrosion, because it has several zones and newish rads.
but could be the overflow pipe.
but didn't do it last year.

that don't make any sense at all

vent pipe is in same place, new rads and several zones so what don't mean anything

so what wasn't their last year CORROSION.

could be a blockage in the f/e tank feed, boiler stat to high or faulty, pump to high etc.

 

[Ratter]

Love the diagram Chris, but they would definitely need to be tropical fish

My system isn't quite that simple because the feed and vent are a long way from the pump which is above the boiler - it'd probably work better if they weren't. Looks like the boiler was moved when the extension was built because it was no longer on an outside wall.

The vent at the moment comes off the cylinder heating coil which is the highest point in the sytem.

I'll certainly have a look around with the magnet at the weekend and see what I can find - a block in the common parts of the pipework seems a good bet.

I may also replace the header tank which is galvanised steel and has seen better days - plastic ones don't rust!

 

[JohnD]

if it's been pumping over, the waterfall will have been picking up air and taking it into your system, with its water and steel radiators.

So even if you didn't have corrosion before, you will have now.

as the water is still able to flow down from the F&E tank into the system, you could add a chemical like Sentinel X400 which will break up corrosion sludge, and will help reduce the blockage. once the pipe is fully blocked, you won't get any water flow over it, so you won't be able to use a chemical to shift it. You will observe that the water goes black, as it starts to break up the sediment which will then be carried in suspension in the water. If badly sludged you can leave the chemical circulating for a couple of weeks to loosen it before you drain and rinse it out.

You will also need a corrosion inhibitor when refilling to prevent further corrosion.

Sadly these chemicals will probably kill the tropical fish you keep in the tank.

If you can post a pic of the place where the F&E pipe and the vent pipe join onto the circulating pipes, and also showing the pump, this will be useful as sometimes the pipe layout is wrong and can be improved.