Where's my slow leak?

[wedge69]

Hi all,

Really hoping someone can provide some suggestions.

We have an Ideal Logic Heat 15 boiler and a Range Tribune HW cylinder all on a sealed heating system. The pressure gauge is up in the airing cupboard with the cylinder and the boiler is downstairs.

When I first turned the heating on one radiator was full of air so I bled it and topped up the system to 1 bar. Six weeks ago the pressure had dropped a bit and there was more air so I did the same.

I found a radiator where the bleed valve was loose so I tightened that up.

Since then the pressure dropped to 0.8 bar, but all radiators were roasting hot so I don't think they had air in.

Last weekend (without bleeding anything) I topped the pressure back up to 1.0 bar, but this weekend it is back down to 0.9.

So to summarise:
I'm losing about 0.1 bar a week.
I have no visible leaks.
I don't seem to have air in the radiators
Nothing is dripping from the tundish
The pressure never seems to go lower than 0.8 bar

One interesting thing Is regardless of whether the pressure is 0.8 or 1.0 cold it never gets above 1.3 when hot.

Does anyone have any suggestions before I get the professionals in? Or is this just normal?

Many thanks.

 

[kidgreen61]

It doesn't sound as though you have a leak, so don't worry about it.

It may be worthwhile checking the charge in your expansion vessel - see FAQs at the top of the page.

 

[doitall]

When the rads are cold pull the valve caps off and check for any weeps, there may be signs of staining on the pipe as well

 

[wedge69]

Thanks.

It's plastic pipes, would they get residue on?

I'll take the caps off though, I hadn't thought of that.

 

[doitall]

You'll have a small weep somewhere, The radiator valves are the obvious then any compression nuts.

 

[ianmcd]

you are looking for a problem that does not exist, the pressure will always vary slightly depending on what temperature the water is at

 

[doitall]

you are looking for a problem that does not exist, the pressure will always vary slightly depending on what temperature the water is at

Thats the answer I'd expect from the installer that is trying to bullshit the custard.

Pressure the system to 1.5bar and watch it drop even quicker.

 

[wedge69]

I appreciate everyone's input, I really do. Before, I checked again and it had gone down to 0.7, however the heating has just come on and it is back up to 1.3 again. The maximum always seems to be constant.

The heating us due to go off again soon, so I'll see how low it goes this time and let you all know.

 

[doitall]

If you top the pressure up with the system cold, it should never go below that pressure, unless there's a leak however small.

And if you are continually adding more water it proves the point and will eventually cause sludge and corrosion in the system.

 

[wedge69]

Yes, that was my thought. However, I don't understand how the pressure always goes back up to 1.3 regardless of what it is when cold. That's what's puzzling me the most.

 

[doitall]

The pressure will always rise as it gets hot (as above ianmcd post).

 

[wedge69]

I understand that. But, surely the hot pressure should be different if I start at 0.7 instead of 1.0? How do they both go up to 1.3?

 

[doitall]

0.1 of a bar is probably around an cup of water, it ain't gonna make much difference in the short term

 

[xr4x4]

Sounds like you have a very small leak.

This will be hard to find as it will evaporate fairly quickly on hot pipes.

I had the same problem as you, pressure would drop over a very long time, turned out to be a slight seep from a rad valve, it was coming from the spindle.

 

[wedge69]

So is the best bet still just to investigate each valve?