unexplained boiler pressure drop

[cazkent]

Have Warmflow 70/90 combi oil-fired boiler and first experienced pressure loss to 0 before Christmas.
Boiler engineers replaced expansion vessel but no change. Advised boiler working so must be leak in pipes losing "a bowlfull" of water every time pressure drops.
Engineers put valves on pipes to cut off downstairs heating circuit. Pressure held with heating upstairs only so confirmed boiler all working and leak deduced to be in downstairs circuit.
Thermal imaging located a leak. Chemical sealant injected but no effect. Floor lifted - found no evidence of there ever having been a leak.
Had downstairs circuit tested with gas. No evidence of a leak at all.
Still losing pressure 1.5 bar to 0 in 5 hours.
Other engineer put balloon on overflow pipe and got golf ball sized water loss.
Boiler engineer adamant it's pipe leak, leak detector says not. Where do I turn? Am now £1,200 out of pocket with boiler engineer costs, leak detection and floors up.

 

[The Baker]

If the overflow pipe you refer to is actually the over pressure relief valve then it should not be passing any water at normal operating pressures. (up to around three bar)

Changing the valve is neccessary before you go any further. (and do not using it as a drain point)

Tim

 

[cazkent]

thank you. I will get the boiler engineer in on Monday. Why would this not be a problem when we are just heating the upstairs radiators?

 

[The Baker]

Why? well at this stage I don't know, but there are various reasons why it did not leak when upstairs only was under test.

The thing about testing for a small volume loss is that you need to test over a long enough period, from what you have said, that would be five hours.

What I can be sure of is that the Over Pressure Valve should not release any system water below 3 bar, thats what I would be sorting out first.

Tim

 

[simond]

thank you. I will get the boiler engineer in on Monday. Why would this not be a problem when we are just heating the upstairs radiators?

The reason is that there is less volume of water in the system when only upstairs is connected. As the volume of expansion is proportional to the amount of water heated, a half knackered expansion vessel might cope with smaller numbers of radiators.

You need a new expansion vessel, the old one is either undersized or partially deflated. There should be no water emitted from the emergency relief pipe, you 'golf ball' tells us what we need to know.

 

[cazkent]

the boiler engineer just phoned. he's suggesting now putting a second RPV on the outlet pipe - and if the first rpv is no good, it will show as a loss of pressure. still seems to think the loss of pressure in the system is too great fpr the rpv - still beleives its a leak. However, leak engineers has gas tested and the pipes hold 3 bars for 8 mins - ie no leak in the pipework. Help !

 

[cazkent]

The boiler engineer has put a pressure gauge outside on the outlet pipe which I'm told should have registered if a faulty PRV had released pressure. I have lost 1 bar pressure over 3-4 hours but there's zero reading on the gauge.

So, I have a new expansion vessel, no apparant problem with the PRV and gas testing has found no leaks in the pipework. Everyone is scratching their heads. Any ideas?

 

[Kayte]

Hi. I know this post is old but I really wonder what the outcome of this was. I have exactly the same problem now and am tearing my hair out to solve it. We have had heat exchanger and prv in boiler repaired but still are losing pressure very rapidly ( although speed of pressure loss is changeable which is also odd)
Had full leak detection done on CH revealing no leak.
If you have any advice to offer I would be very grateful as am going round in circles trying to sort.
Thanks very much!

 

[The Baker]

From what you say you bloke has carried out what seems like a thorough job.
So fixing via the forum may be difficult. But as a start what boiler do you have.