HW cylinder boiling over?

[dennyboy]

Hi all - bit of advise please
had a job through today to replace a fortic indirect cylinder, after speaking to the householder, It seems hes had a heating engineer out to the cylinder on 3 occasions in the last week, each time the cylinder had boiled over and flooded the hallway - heres what he replaced;
the 3 way valve
the ball-valve
tried putting a better fall on the overflow pipe?
after the 3rd time he told the householder that there was probably a crack in the coil that was causing it to boil over? - first time I've heard of this? - checked the hot water coming through the taps and it wasnt discoloured/rusty etc - he said he checked the cylinder stat and it was shutting off the boiler when it should have and the immersion heater isnt working and not used anyway so I dont think its that - any ideas chaps? - the only thing I noticed on the cylinder is the overflow outlet is higher than the ballvavle (half an inch from the top of the header-tank) hence why it probably flooded out - I'm not bothered about putting a new one in but I've a sneaky feeling that its going to happen in the new one albeit I'll put the overflow in the right place

 

[JohnD]

disconnect the wires to the immersion heater just to make sure

has he got a shower or other mixer tap (basin, bidet etc) where the cold supply is at mains pressure and the hot comes from the tank?

 

[dennyboy]

disconnect the wires to the immersion heater just to make sure

has he got a shower or other mixer tap (basin, bidet etc) where the cold supply is at mains pressure and the hot comes from the tank?

no - no mixer taps in the property? - immersion deffo not working

 

[twgas]

What boiler/system is it?
If the immersion isn't working it's hardly likely to be boiling over, possibly overflowing - if the ball valve is good and there are no mixers the most likely cause is a failed coil.

 

[ajstoneservices]

Could be split coil, check the f&e is it filling. It's not thermal store is it?.

 

[dennyboy]

Cheers Chaps - if it is a failed/split coil wouldnt the cylinder keep filling up, eventually causing it to leak again? and why only when the hot water is on? - if so I better get back in the morning and isolate the supply to the f+e tank

 

[onlyfitidealboilers]

think you need to go back to college!!

 

[dennyboy]

think you need to go back to college!!

who needs college when you've got this place - seriously though I always thought the main sympton of a failed coil was dirty/discoloured water coming through the hot water taps?

 

[onlyfitidealboilers]

depending on which tank is lower the water will rise into that one and the higher one will fill, so therefor in your case the water will rise up into the fortic tank via the cold feed, then out the overflow, but the f&e tank will fill via the cold feed and escapeing out the coil