Central Heating Leak

[chrishutt]

The heat exchanger you refer to is the secondary one. The main (primary) one is above the burners in the combustion chamber.

You're quite right about the slots on the isolating valves.

 

[rwalters]

Cheers Chris, the main one in the combustion chamber has some evidence that there has been or is leakage, there is some signs or green corrosion on it.

 

[Softus]

That's proof that there is a leak fault on the boiler...

Not quite proof, yet. The same effect can be seen if one of the isolating ball valves doesn't shut off AND there is a leak on a CH pipe (or rad valve etc).

I'm puzzled that the pressure didn't rise slightly when you opened the isolating valves, if the system (external to boiler) pressure had remained at 1 bar. You might also have a minor leak there.

Quite so.

As a suggestion, you could (with the system off and cold of course):

1. Pressurise again, to whatever pressure you ended up using last time.
2. Isolate the CH at the two valves.
3. Open a rad vent and reduce pressure to ambient; leave vent open.
4. Wait until the pressure drops to 0.5 bar.

If the pressure on the gauge drops at the same rate as before, then you have a clearer indication that the leak is not in the CH pipework.

However, if the pressure drops more quickly then you have a faulty isolating valve - this would be confirmed by water continuing to emerge from the open rad vent. In this case you can't point the finger at the boiler until the faulty valve is replaced.

Edited - apologies to ChrisR and chrishutt, both of whom already mentioned the leaky valve possibility.

 

[rwalters]

Good thinking softus, will give that a try too.

 

[rwalters]

Softus,

The isolation valves are obviously "passing by". I pressurised the system to 2bar, closed the isolation valves and let water out of a radiator upstairs. Came back downstairs and the boiler pressure has dropped, so one or both of the valves are not sealing properly.

 

[Softus]

The isolation valves are obviously "passing by". I pressurised the system to 2bar, closed the isolation valves and let water out of a radiator upstairs. Came back downstairs and the boiler pressure has dropped, so one or both of the valves are not sealing properly.

This doesn't seem conclusive evidence to me - did the water that you believe passed through the closed isolating valve(s) drip from the rad vent?

 

[rwalters]

The isolation valves are obviously "passing by". I pressurised the system to 2bar, closed the isolation valves and let water out of a radiator upstairs. Came back downstairs and the boiler pressure has dropped, so one or both of the valves are not sealing properly.

This doesn't seem conclusive evidence to me - did the water that you believe passed through the closed isolating valve(s) drip from the rad vent?

Yep, water just kept coming.....

This is the procedure I did.

Opened isolating valves
Pressurised system to 2 bar
Closed isolating valves
Bled radiator upstairs until water just trickled
Went back downstairs, boiler pressure dropped by about 1 bar

Surely, if the valves were remaining sealed and closed, the pressure on the boiler side should have stayed constant, but only dropped when I re-opened the valves.

 

[Softus]

Opened isolating valves
Pressurised system to 2 bar
Closed isolating valves
Bled radiator upstairs until water just trickled
Went back downstairs, boiler pressure dropped by about 1 bar

At this point you don't know whether the valves leaked or the boiler leaked.

Surely, if the valves were remaining sealed and closed, the pressure on the boiler side should have stayed constant, but only dropped when I re-opened the valves.

No - this is still inconclusive.

I don't know why you didn't just use the same parameters as before, i.e. 1 bar, and measure the time it takes to drop from 1.0 to 0.5 bar - that way you can compare the two results and draw a conclusion.

Bear in mind that you might have two leaks - this is why leaving a problem unfixed is generally a bad idea - "a stitch in time saves nine".

 

[rwalters]

Softus,

The boiler, under normal circumstances takes about 24 hours to loose .5 bar of pressure, with the test I just did, it dropped by 1 bar straight away, within minutes, so the isolation valves are not doing their job properly are they ?

 

[Softus]

The boiler, under normal circumstances takes about 24 hours to loose .5 bar of pressure, with the test I just did, it dropped by 1 bar straight away, within minutes, so the isolation valves are not doing their job properly are they ?

I agree, now that you've said how long it took!

Next step - replace the valves. Or you could cap the CH return and couple up the flow to the mains, with a pressure gauge on it, and pressurise it independently of the boiler to see if the pressure drops.

 

[ididdidi]

Just a quick observation you are closing the correct valves on the flow and returns and not say a return and gas isolation valve which would give the same results that you are getting.

 

[rwalters]

Just a quick observation you are closing the correct valves on the flow and returns and not say a return and gas isolation valve which would give the same results that you are getting.

I know I might not know much about boilers, but I know a little about plumbing , yes, did close the right one. The 2 big thick pipes on the outsides of the row of pipes. They go from left to right, 1 - CH, 2 - DHW, 3 - Gas, 4 - Cold Water In, 5 - CH, I isolated 1 and 5.

 

[chrishutt]

All very strange! You could try the relative pressure drop test in reverse -pressurise whole system to 2 bar, close isolating valves, drop pressure in boiler to near zero, then check pressure in pipework by opening vent point higher up. If water comes out under pressure then the system side pressure will not have dropped (much).

If you're up to it you could fit a couple of 22mm iso valves on the flow and return pipes just below the boiler valves. You could then be quite sure that the two parts were isolated.