Vent pipe leaking

[llew]

Water keeps flowing out of my header tank overflow.
It only happens when the heating is on, even if the room stat is set to low (off).
The water is coming up the vent pipe, filling up the tank and making it overflow.
Have changed the boiler stat, and tank stat (just in case). When set on water no problem once heating turns on, and if i do not use the water, I get the overflow

 

[chrishutt]

Blockage in pipework, probably near feed connection. System will probably need major flushing and cleansing. You could try a DIY approach (see Wiki or FAQ topic) or get a quote for power flushing.

 

[llew]

Thanks Chrishutt, last night it leaked without the heating on, seems to be temperature relatated If boiler stat is up at 60 and no water drawn off it leaks.
I guess the water is being forced up the vent pipe because it is the line of least resistance ie avoiding the blockage

 

[chrishutt]

You guess right. When the water is heated it expands. This expansion is normally accommodated in the feed and expansion tank, but if the feed pipe is blocked that expansion will push up the water level in the vent pipe until it overflows.

 

[doitall]

One really should ask where all this water is coming from.

A make and model of the boiler, Combi or cylinder may be handy as well

 

[chrishutt]

Good point DIA, but I'm assuming the feed pipe blockage is partial and the water that discharges out the vent is slowly replaced via the feed, but that doesn't really fit with the expansion not feeding back up the feed pipe, does it? Could we have a leaking coil here?

 

[doitall]

Possibly Chris but it would doitall the time and not dependant on hot water or heating.

Plate heat ex could be an option.

 

[JohnD]

Coming up the vent pipe signals a blockage (what odds on the Tee where the 15mm F&E pipe joins the 28mm near the pump?), but overflowing suggests too much water as well.

Is the float valve set to give a "cold" water depth of just a couple of inches on the F&E tank, so there is room to accomodate expansion? Have the rads been bled (as gas expands a lot more than water, and pumping over will cause corrosion)?

 

[llew]

Cylinder system.
The boiler is a Glowwarm Ultimate 50FF.

A rad developed a pin hole leak during winter, I replaced this and treated the system. Leak did not start till couple months later, suspected ball valve in the hot water feed tank was leaking, causing overflow, replaced this but problem remained.

The overflow gets worse, increased water leak, the hotter I set the tank stat. Noticed that when the boiler fires there is a lot of bubbling and gurgling (air) coming from it.

There is defiantly water flowing up and out of the vent pipe and it keeps going, the only thing I can do to stop it is turn the system off or run off a load of hot water.

The system is about 10 to 12 years old, I do not have any history of it.

 

[doitall]

Are you saying the larger storage tank ballvalve is running all the time.

Is the smaller header tank lower (water level) than the storage tank.

Yes to both questions mean the cylinder coil has gone.

 

[llew]

no ball valve not going all the time, crazy flat roof means I could not easy check it, so i replaced it.

This eliminated the ball valve leaking. I suspect the blockage theory.