0.5 bar/per hour pressure drop on system boiler

[mickyg]

have you looked outside?? there should be a pipe coming through the wall by your boiler that terminates with an open end. This should be dry. This is the prv termination.

 

[DJS1]

Yep, pipe outside is dry.

Looks like you can't easily isolate the DHW as the flow doesn't have an isolation valve - I guess having one could be a bit of a risk. Anyone know if it's worth doing this test by turning off the rising main and the DHW return, or is that a bad idea (with the boiler turned off obviously - just a bit concerned that the CH water could somehow end up being forced into the incoming supply pipe)?

Thanks

 

[EliteHeat]

When I read the op’s first post mentioning that the pressure dropped to 0.5 bar I also thought of a perforated HWC coil, however the post does not make clear whether the pressure always settles to 0.5 bar or would eventually go to zero.

With the system not isolated or running in any way whatsoever it would be useful to check to see if the pressure stabilises at 0.5 and if this decreases when the system starts to run for HW – if it can run at all.

If it does this then it is most likely that the coil is perforated and the 0.5 bar is simply pressure equalisation because of the head of water provided by the cold-water cistern. If though, the pressure drops to zero with the system inactive then your leak is somewhere else.

 

[DJS1]

Thanks for your reply.

Yep, the pressure consistently drops to about 0.3-0.4 bar with nothing isolated and the boiler turned off. It's slightly less than 0.5, but I can't be more accurate than that.

The system has been turned off the last few days for all but a few hours a day and the pressure has never hit zero.

The cold water tank is about 3 metres above the hot water tank, which if my memory serves me correctly is 0.3 bar (10m water pressure = 1bar?) so I did wonder if that might point to the coil.

I'm loathe to turn the hot water on when the pressure's only at 0.3/0.4 bar. Is it safe to do so without knackering the pump etc?

Thanks

 

[EliteHeat]

Thanks for your reply.

Yep, the pressure consistently drops to about 0.3-0.4 bar with nothing isolated and the boiler turned off. It's slightly less than 0.5, but I can't be more accurate than that.

The system has been turned off the last few days for all but a few hours a day and the pressure has never hit zero.

The cold water tank is about 3 metres above the hot water tank, which if my memory serves me correctly is 0.3 bar (10m water pressure = 1bar?) so I did wonder if that might point to the coil.

I'm loathe to turn the hot water on when the pressure's only at 0.3/0.4 bar. Is it safe to do so without knackering the pump etc?

Thanks

The boiler might not be capable of firing with the pressure that low but if it is then just try running it for a few minutes on hot water. The idea is that the pump will overcome the pressure from the cold water cistern and pump out into the hot water cylinder, thereby reducing pressure even more. This should pretty much confirm that the coil has a hole in it.

 

[DJS1]

I just turned the hot water on with the pressure at about 0.4 bar and it dropped to zero pretty much instantly.

That seems fairly conclusive, new tank it is then.

Thanks again for your time.

 

[DJS1]

Turned the hot water off again and the pressure popped back up to 0.4 bar which I guess is the cold water tank forcing water back through the coil.

Any more comments welcome if you think a point has been missed, but otherwise, thanks for all your help.

Once a new tank's in I'll post the result so the thread proves useful to future searches.

 

[DJS1]

I thought I'd finish this thread off to say that I've replaced the hot water cylinder and now the pressure is nice and steady on the boiler, so problem solved.

Thanks for all the help