Central heating overflow

[chrism]

Hi, The overflow from my central heating/hotwater expansion tanks constantly 'dribbles' - the overflow just keeps up with the excess water level in the tank! The ballvalve and the expansion pipe are all OK - no water/steam from the pipe and the ballvalve is not leaking/dripping also it is set to 1 inch below the overflow etc. The excess water is mysteriuosly coming out of the feed pipe to the central heating system - all the time the heating is on - just a small flow but enough to fill the tank eventualy up to the overflow pipe. The pump is set to the middle setting and everthing else seems to work all ok

any ideas?

chris

 

[AnonymousImport]

Could be a split in the coil in the hot water cylinder.

(Not good)

 

[simon]

A split in the coil would normally show itself as discoloured water in your hot bathroom taps.It couls also leak chemically treated central heating water into those same taps.(also not good!)

 

[chrism]

Thanks for the tips.
I have not noticed any water disclouration via the hot taps etc - but then again if the central heating circuit is leaking in to the hot water circuit I suppose the small amounts may not notice - also the water in the rads etc would be replaced eventualy with clear fresh water!

Is there any way of testing the coil - with out taking the tank apart - say a pressure test or something?

Chris

 

[simon]

tie off the f&e ballcock and don't turn anything on.If water comes into the f&e tank through the overflow it can't be coming from anywhere else

 

[chrism]

Thanks for the info. It looks like thats the problem then. If I connect a cold tap (mains pressure) via a hose to a hot tap (near the tank) turn them both on - then the cold should 'squirt' out of the hole in the coil - thus giving a noticable and thus confirmatory diagnoses of the problem - won't it?

 

[simon]

not sure...personally if I had a immersion in the top of the tank I would shut the cold feed drain the ch take it out and then see if the level of water in the tank dropped.Otherwise I'd shut the mains water to the cylinder drain the ch til the flow stopped then turn the feed back on...any more flow from the drain off do a bit of overtime and get a new cylinder.If your cylinder is in good nick you may be able to replace the coil if you think it's worth it!

 

[OTTOSMARM]

Just a thought for you... I had a similar experience with my central heating overflowing around this time last year. My heating system used a thermal store, in which the role of cylinderand heating coil are transposed. ie The cylinder is heated directly from the boiler, and the coil, which is smaller in bore, in fact it is a double bore which is finned, and is very long, and this carries cold water, at mains pressure, through the mass of hot water in the cylinder, thus being heated. I discovered that the expansion tank, which sits on top of the cylinder, was full of hot water, because the cylinder had perforated and was leaking into the expansion tank from below. It must have been like this for some time but only came to light when the coil began to leak, very slightly, thus introducing extra water into the system. This happened on a system in a new house that was just under 10 years old, in a very soft water area, and the builders had not fitted corrosion inhibitor. Cost to replace?? try 750 quid ex-factory!! I now have a conventional system fitted in place.

 

[chrism]

Thanks for the thoughts. Looks like a new hot water tank then. They seem to be circa £100 + vat - sound about right?

Fitting looks fairly easy - drain - unscrew connecting pipes - screw in new - fill. Is that about right - or is it normally a horrendous job?

 

[simon]

That's about the mark.
Fairly simple job for a plumber, its the draining and refilling that's a pain.You may need a bit of soldering to make it fit and it's always hit and miss as to weather the old immersion will come out, best to spend £15 on a new immersion and thermostat.