Expansion Tank Overflowing

[RPDS]

Sorry if this sounds straight forward but I have an Indirect central heating system and hot water pours out of the overflow pipe of the expansion tank when the hot water is on and the central heating is off.

When hot water is on and central heating is on, it doesn't overflow at all. I got rid of loads of the water in the expansion tank so it was just covering the pipe and adjusted the ballcock accordingly, but within 24 hours the tank was full and overflowing again.

Any help or ideas you could give would be greatly appreciated.

Thanks

 

[Gray0689]

Your hot water is pumping over
Try turning your pump speed down by 1

 

[RPDS]

Hi Gray0689 thanks for your quick response. I'll give it a go as soon as I can find it!

 

[dboi78]

hi gray,

can u explain what u mean by pumping over !! do u mean out the vent ?? if so does that mean the pump position should be altered to after the vent and feed ??

just an interested observer.

 

[RPDS]

Hi, turned the pump down as suggested, but it's still pouring out of the overflow. I'm stuck on this one so would appreciate any help. Thanks very much

 

[mjt]

is the expansion tank higher or lower than the CWSC in the loft?

if it is lower you could have problems with the coil in the cylinder

 

[RPDS]

I would say they are on the same level, but I can't say 100% because they are in different loft spaces. How would it affect the coil? (Sorry if it sounds stupid but I'm wanting to learn as well as fix the problem)

 

[mjt]

No worries we have all been there!

the coil that runs through your coil in hot water cylinder is a separate from the water thats in the cylinder - however if there is split/hole in the coil then water could get into the heating circuit and work its way up the cold feed from the expansion tank and cause it to overflow.Especially if the CWSC is higher than the expansion tank as its greater head will force water up.

If this is the case then it means a new cylinder

 

[SimonG]

I wouldn't be going the new cylinder route just yet.

Is it S Plan or Y plan, i.e. is it two port vaves or do you have a three port valve?

Have you had any work done recently on the plumbing?

To test if it is the cylinder, turn heating and hot water off and monitor water level within f & e tank, leave it off for as long as possible, if it doesn't change then its not the coil.

 

[mjt]

the cylinder you would hope to be the last option of course - as you say it is easier to check for this first

 

[Ultimate P & H]

The other thing to check is scale build up at the point where the cold water from the expansion tank meets the hot system water. Usually thats a tee on the boiler flow, after the open vent pipe but before the pump. That point on the system is THE most likely point for a scale build up.

An easy although not 100% conclusive test is to put a small magnet on the tee, often in an untreated system ther will be ferrous corrosion as well as scaling and the iron gets trapped in the scale, if it sticks there is a build up, I've seen a 22mm pipe bore reduced to less than 5mm in the past. If you've eliminated the other possibilities and the system is more than 5 or 6 years old I'd be inclined to cut the pipe work out in that vicinity and inspect. If scaled then I'd advise running a descaler and cleanser through the system before flushing and inhibiting.