Discharge from unvented system

[euan]

I live in a block of flats built new about 7 years ago. Unvented system, gas boiler (Potterton I think).

There are 3 flats, one above each other, and copper discharge pipes come out at each level, join a common downpipe, and terminate just above the ground at the bottom. From looking at the outside of the block, as far as we can tell, only our 3 flats are joined to this particular common downpipe.

There does not appear to be any pattern to the timing of the discharge, but when it does come, there are pretty steady drips (enough to form a pool of water outside my garage!)

2 of us in the 3 flats have checked the visual overflow/tundish thing in our systems when the dripping has been going, and apart from a little condensation moisture, there is not nearly enough to cause the level of water coming out outside. The third flat kindly shut their boiler off, ran their tank dry, and the drips were still coming out.

There doesn't seem to be anything coming out of our systems from looking at the visual thing, so I am stumped.

Any possible ideas?

 

[PEDANTICVINDICTIVEMAN]

I had a similar problem when I went to a house, it LOOKED looked like there was no discharge in the tundish but when I put my finger through the holes it was running at a reasonable pace, have another check.

 

[IanDB]

Is this the outlet associated with the hot water tank? With an unvented system you have to recharge the air gap in the tank periodically otherwise you will get this slow drip.

 

[euan]

We've all stuck our fingers into the tundish (not entirely sure this was a safe thing to do if boiling water coming out but anyway...) and there is nothing discharging.


Dont'd know about this airgap thing - what should I be doing periodically?


I'm beginning to wonder if something else is connected to the discharge pipe below the level of the tundish and hence we can't see the discharge. Can't really tell as once the discharge hits the floor it goes underneath the boards until it goes through the wall.

There is a boiler discharge, abut the boiler is on the other side of the house and appears to have it's own discharge.

I amy have to buy one of these pipe detectors and trace the pipe run to the outside to see if there is sonething joining it.

 

[ChrisR]

We need to know if you have an "unvented hot water storage system" and what type. Is there a name on the side of the HW cylinder?
Do you have high pressure hot water? Is there a separate pressure vessel
connected to the water pipes? That would be a tank a foot or so across, probably white or blue.


The cold water will go into your hw cylinder at the bottom. If you trace that pipe up, do you see it going to some lumpy valvy bits? (Sorry for the technical terminology!!)

 

[MANDATE]

Would the boilers be combis, because in a combi system the water in the central heating is pressurised to about 0.7 bar when cold and this increases to about 1.7 bar when hot. There is also a pressure relief valve should the pressure reach 3.5 bar. As soon as the pressure drops to less than 3.5 bar the valve closes again. Now it could be someone has too high a pressure when cold making the valve open when hot.
Or the pressure rise is well over the norm making the valve open when hot.
Pressure relief valves are obviously a safety requirement on pressurised systems, on unpressurised systems where water cisterns (tanks) are used then the problem relates to faulty ball cocks when the water level rises and water is discharged thruogh a overflow pipe at a constant rate.