Expansion tank overflow

JMJ · 11 Mar 2006

Our expansion tank overflows on a rather regular basis into our garden.

I assume related is a rather large amount of air that accumulates in the upstairs radiators, so I bleed these regularly.

The house is old, so it can be assumed that the radiators are probably from the early 70s. Boiler is less than five years old.

The problem started 2 years ago when we had some plumbing work done - new bathrooms, a radiator resited, and the HW tank replaced with a Megaflow. It seems to be getting worse (discharges are more frequent now).

Apart from the air and overflow, the system works well at keeping us warm.

Any ideas as to the DIY things we can try before calling in the experts?

Thanks

Some extra info:

The boiler is a Potterton Kingfisher MF, located on kitchen floor.

The pump is a Wilo Gold 50, located next to the boiler.

Megaflow is in the room directly above the boiler, and the F&E tank is in the attic directly above that.

B.O.B DOLE · 11 Mar 2006

JMJ said:
Our expansion tank overflows on a rather regular basis into our garden.

I assume related is a rather large amount of air that accumulates in the upstairs radiators, so I bleed these regularly.

The house is old, so it can be assumed that the radiators are probably from the early 70s. Boiler is less than five years old.

The problem started 2 years ago when we had some plumbing work done - new bathrooms, a radiator resited, and the HW tank replaced with a Megaflow. It seems to be getting worse (discharges are more frequent now).

Apart from the air and overflow, the system works well at keeping us warm.

Any ideas as to the DIY things we can try before calling in the experts?

Thanks

Some extra info:

The boiler is a Potterton Kingfisher MF, located on kitchen floor.

The pump is a Wilo Gold 50, located next to the boiler.

Megaflow is in the room directly above the boiler, and the F&E tank is in the attic directly above that.

have you checked the ball cock valve in the expansion vessel

JohnD · 11 Mar 2006

And if you are bleeding air out, you are having corrosion. Has it got a chemical inhibitor in it? If not, then (at least) give it a clean and inhibit.

brumylad · 11 Mar 2006

yep, new ball cock in expansion tank first.

JPC · 11 Mar 2006

if the f and e is constanly filling up with fresh water from a drip or 2 from the ball valve do you think the inhibitor it might have had would still be as efficient after 2 yrs.

does the fresh airy water thats dripping in all the time contribute to corrosion

or do we think the water in the f and e does not actually get to circulate around the system ?...(genuine question)

JohnD · 11 Mar 2006

It takes time, but every day some water rises into the tank when the system gets hot and expands, and some passes down when it gets cold, so not only does the inhibitor get diluted, but you may also get additional corrosion because the "new" water will have more free oxygen in it.

When you had your last plumbing work done, the system should have been cleaned and refilled using new inhibitor.

You mentioned the cylinder was replaced so it should be unlikely that you have a leak in the coil (if you do, then the water from the hot tap supply can leak into the circulating water, causing the F&E to overflow even if the ball cock is closed).

Try sitting in the loft with your torch and see if the ballcock is dripping. adjust it so the water level is very low in the F&E and thus gives more capacity for expansion.

(anyway, fit a new ballcock, they're cheap enough)

Softus · 11 Mar 2006

JPC said:
if the f and e is constanly filling up with fresh water from a drip or 2 from the ball valve do you think the inhibitor it might have had would still be as efficient after 2 yrs.

does the fresh airy water thats dripping in all the time contribute to corrosion

or do we think the water in the f and e does not actually get to circulate around the system ?...(genuine question)

Personally, I'm not experienced with Megaflows, but I take it that you have a pressurised DHW system with an indirect open vented heating system.

It seems to be that you're making the mistake of getting easily distracted from the main problem. Eliminate problems one at a time until they're all gone.

Until all problems are fixed, it doesn't matter whether or not the fresh water contains air and/or dilutes the inhibitor.

So, the F&E cistern is overlowing - symptom #1. The float valve in the F&E is not shutting off - possibly the cause of symptom #1.

You haven't said whether or not the drip rate from the valve is the same as the rate of overflow, but you should service or replace the valve, then see if you still get water overflowing. If so, then you have a second fault.

If not, then I would drain two cisterns worth of water out of the heating system and add a new does of inhibitor.

Oh, and BOBD - expansion vessels don't have float valves; feed and expansion cisterns do.

Gasguru · 11 Mar 2006

Apart from checking valve shutoff a very common reason is incorrect water level when the system is cold.

With radiators cold the water level should be around 25 - 50mm above the feed outlet (this should only be around 25mm from the bottom). This is normally achieved by bending down the brass float arm. This allows the water to expand without rising to the overflow outlet.

Another but rare problem is a punctured float - unscrew and check its not full of water.

Since the cistern has been overflowing and drawing in fresh water each time the heating is on you may now have severe corrosion which you will need to deal with to prevent other problems.

JMJ · 11 Mar 2006

Thanks everyone - these are all very helpful responses.

It is a Megaflo with an open heating system. Not sure if that is kosher or not, but it was just a straight replacement of the old vented tank for the new Megaflo.

I think I am leaning for having someone in to look at it, but I wanted to do a bit of detective work first myself.

At the moment, the overflow is like Old Faithful. It is not a drip but a full arc of water lasting for over a minute. Recently, it has been several times a day but I noticed that the boiler was up full (had run out of hot a while back so cranked it up and forgot to return it to the mid point). Have also turned down the pump, having read a few other topics here.

I'm happy to replace all of our old radiators, but obviously don't want to damage the Megaflo and the newish boiler.

Is there anything to be gained from draining the system and refilling with fresh water?

Softus · 11 Mar 2006

Gasguru said:
This is normally achieved by bending down the brass float arm. This allows the water to expand without rising to the overflow outlet.

Oh. So you're the one. Why not install a Part 2 float valve and arm at the correct height, and adjust it to give the correct water level?

JMJ said:
At the moment, the overflow is like Old Faithful. It is not a drip but a full arc of water lasting for over a minute.

This sounds more like pumping over, which can be either too high a pump speed and/or a sludged up system.

JMJ said:
Recently, it has been several times a day but I noticed that the boiler was up full (had run out of hot a while back so cranked it up and forgot to return it to the mid point). Have also turned down the pump, having read a few other topics here.

So - what was the effect of turning down the pump?

JMJ said:
Is there anything to be gained from draining the system and refilling with fresh water?

No. No until you've fixed the problem. If the problem is sludge, then you need to flush the system, not just drain and re-fill it.

JohnD · 11 Mar 2006

it's been said

JMJ · 11 Mar 2006

Softus said:
[So - what was the effect of turning down the pump?

Just did it a few hours ago, so will observe over the next few days.

Thanks for your help

Gasguru · 11 Mar 2006

Softus, I only use Pt2 valves - we all Know PT1 valves contravene water regs unless fitted with double check valve.

Even with Pt2 valve you may need to bend arm.

However the majority of valves I see fitted and continue to be fitted (illegally) are Pt1

Softus · 11 Mar 2006

JohnD said:
it's been said

Whatever "it" is, it's been ignored, so it's worth saying again.

Gasguru said:
I only use Pt2 valves

Fair play

Gasguru said:
Even with Pt2 valve you may need to bend arm.

Not if it's installed at the correct height for the amount of water in the system.

Gasguru said:
However the majority of valves I see fitted and continue to be fitted (illegally) are Pt1

I concur; hence my comment about fitting a Pt2 one, and fitting it correctly.

JohnD · 11 Mar 2006

Softus said:
JohnD said:

it's been said

Click to expand...

Whatever "it" is, it's been ignored, so it's worth saying again.

You misunderstand, I'd written something; while I was typing away, you'd done yours, so I went into edit and took mine out, as superfluous

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Expansion tank overflow

B.O.B DOLE

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