central heating loses pressure at night but not in the day

[terryplumb]

Did you close both valves on every radiator ?

 

[Colin Green]

Did you close both valves on every radiator ?

Yes, except 2 in the loft conversion. I turned everything fully anticlockwise which is off for the other 8 rads. Except these two. Doh!

 

[terryplumb]

Fully ANTI clockwise would open them fully ??

 

[MeldrewsMate]

Fully ANTI clockwise would open them fully ??

That depends on whether you're above or below the valve

Colin, you seem to have shown that over a single night, and with all rads (except two) isolated, you get almost zero pressure drop, thus indicating that the pipework was not the cause of your overnight pressure loss on that occasion, nor the two rads inadvertantly left on.
I suggest you work methodically to find the cause, using the following method:

1. Repeat the exercise that caused zero drop. Does it have the same zero drop every time (5 repeats should be enough)? If so, great, if not then your test method is suspect.
2. Try again but without isolating the boiler.
3. Leave out one radiator from the process for each subsequent test until the pressure drop recurs. That will be the cause of the drop.

MM

 

[Colin Green]

I thought I had it. All on except the living room and downstairs toilet radiators. No pressure loss for 2 days and 1 night. Tried it for a second night and the pressure had gone. I have the week off this week so I'll be taking up some of the floors to see what I find.

 

[Colin Green]

I've cut 5 test holes in the floor today, all of them right over the pipes. Result! Two inspection sites are where the pipes from the living room rad go under the floor. The pipe is bent, rather than joined with an elbow. As are the dog legs that take it under the door. The other 3 sites are in the hall. One where the pipes come down inside a stud wall, and one on each door. I can put my hand on the T joints where the pipes split for the dining room and living room rads.

All of the pipes are dry and look in good condition to me. Nothing that looks like a leak. What should I be looking for? Corrosion?

The cavity under the floor is about 20cm deep and a mixture of wet earth and builders rubble. No point looking for a damp patch.

 

[jackthom]

Don’t think you’ve given any info on what age or sort of house you have but would you reasonably expect the area under the floor to be damp or could that be a result of the losses from the heating?

Should say I think it’s unlikely the radiators or their valves are the problem; I’d expect it to be fairly obvious if they were leaking so much water.

 

[Colin Green]

Don’t think you’ve given any info on what age or sort of house you have but would you reasonably expect the area under the floor to be damp or could that be a result of the losses from the heating?

Should say I think it’s unlikely the radiators or their valves are the problem; I’d expect it to be fairly obvious if they were leaking so much water.

It's a 1930s semi with a suspended wooden floor. The floor was replaced with large MDF boards with Celotex glued in between the joists 4 years ago after the whole house was replumbed and rewired. I think it reasonable that the soil beneath the house is damp during a rainy October.

 

[kidgreen61]

Are you able to disconnect your condense pipe from your boiler easily, (assuming it has one) ?
As said earlier, the HEX may be leaking, the condi pipe will drip with boiler switched off if that is the case.

 

[plumberbuckscounty]

Due to the complex nature of modern plumbing, this can be one of the hardest problems to identify. Most pipework is hidden within walls or behind cupboards or panels, meaning it is very difficult to conduct a visual examination. However, even if leaks are hard to pinpoint, it is very important to find them, and over time they can cause damage. This can range from unsightly mould to more advanced rot problems, leading to more expensive damage.

 

[Colin Green]

Meet my new friend Sentinel Leak Sealer. 2 days in and no leaks. I'd rather have found the leak and fixed it properly, but ripping up a Karndean floor to see if the leak was under it didn't seem like a good idea. Putting gunge in the pipes does seem to have worked. Thanks everyone for the help and advice.

 

[Mottie]

I sometime chuck a can of stop leak in cars when I just can’t pinpoint the leak.