Leaky pressurised heating loop

[Ron Lowe]

Hi, All.

Our CH is loosing pressure. At an anoyingly slow rate.

Half a bar a week or so.

Means that every 2 weeks or so, I need to give it a quick top-up after the boiler has locked out for under-pressure. THat involves a trip outside ( usually in dressing-gown ) to the garage on the lower level.

I'm of the opinion that the leak rate is so low, that even with visible pipework, it would be hard to find. WIth pipework inaccessible, I might as well just live with it unless the leak rate becomes substantially worse.

It's not leaking from the boiler PRV.

I've considered building an 'auto-fill' device, involving pressure and temperature sensors, and timers. It would come on at pre-defined times, when the system is cold, and below a lower threshold pressure. It would open the solenoid valve untill the pressure reached an upper pressure threshold ( or a 10-second timer times out to prevent flooding if major leak ).

Anyone tried anything similar?

[Chris Bartram]

You could just check it every week to stop the lock-out.

[cynic]

Commercial pressurisation units such as you describe are already on the market.

[Roger Mills]

Aren't there some products on the market which you can add to the water in the system to seal minor leaks?

Failing that, why not top it up more often (while fully clothed!) without waiting for it to lock out?

[Onetap]

The top-up water is bringing limescale and oxygen in to the system, and will cause corrosion and sludge problems over time, so ideally should be sealed; but you know that. Check all the exposed rad valves and pipework; because you are dreading a leak under an inaccessible floor, one tends to assume that is where the leak is. A small leak can evaporate from hot pipes, leaving only stains behind.

The only means of legally connecting the mains water to a heating system is through a reduced pressure zone valve, the appropriate device to prevent back-siphonage of the fluid (Cat 3?) into the water mains. These are available commercially but are very expensive and should be installed and commissioned by someone with the relevant ticket. Solenoid valve gadgets with pressure switches can be done, but not legally under the Water Regulations.

Pressurisation units have a break tank and a small 12V (usually) pump operated by start and stop pressure switches. I have one that I use occasionally for anti-freeze and stuff; useful (to me) does exactly what it says on the box and all legal.

You could put in an additional pressure vessel(s) to give a longer interval between top-up and shut down.

[Ian Jackson]

Is there the equivalent of 'Radweld' available for CH systems? It's ages since I've had to use it in a car*, but it does work well provided there is no flexing where the leak is.

*Remember the good old days when car radiators all leaked (outwards) and windscreens, doors and boots also all leaked (inwards)?

[Roger Mills]

Yes, Screwfix do a variety of products by Fernox and Sentinel - such as

years ago, I used some Bar's Leaks stuff intended for cars (still seemingly available) in my then (vented) CH system, and it worked perfectly.

[geoff]

In message , Ron Lowe writes

Sounds a lot of faffing about for something you could do maybe once a week manually. Are you going to get it to deliver a measured amount of inhibitor at the same time ?

[Andrew Gabriel]

Wait until the heating is off and the system cold. Then pressurize it up to it's normal hot pressure with cold water. This will cause it to leak at its normal leak rate, but being cold, the leak isn't going to dry up and may then be locatable.

Actually, this is something I do every few years as part of the system servicing. I usually find a couple of radiator stop valve shafts which seep and I swap them out, even though the leak isn't yet bad enough to emerge from under the cap.

The other place I've found a leak is the O-ring seal on a radiator bleeding plug, but that was just after I had removed and refitted it to add inhibitor - it didn't seal after refitting.

[andrew]

Commercial systems I work on have "mini-fill" auto top up with built in pumps.

One biomass district heating system, supplying 54 dwellings, which I visited had simply left the mains flexi tail connected ;-(

AJH

[Ron Lowe]

Correct. But usually at inconvenient times because I've forgotten.

Are you going to get it to deliver a measured amount of

Precisely the same amount as the manual re-charge.

The volumes involved are very small. The dilution will occour either way, but I'm not over-concerned in the medium-term. I may manually add some every year or so.

I may look into some of the rad-weld type products ( ISTR that egg-based solutions used to exist... )

[Ron Lowe]

Well yes, if the pipework was visible!

It's underneath the flooring. I'd need to lift ALL the flooring in ALL of my house! That's just not going to happen.

I've already done this for all the visible and easliy-accessible pipework :-(

Yes, I know what you mean. But it's an inherent flaw in sealed systems.

No system of pipework that snakes around a house is 100% pressure tight. Over time ( days / weeks /months /years )the pressure *will* drop. It's just a matter of what you can live with.

Hassle of finding-and-fixing versus hassle of re-filling.

I'm probably going to DIY an auto-filler. It will probably be against regs.

[Onetap]

Oh yes, and solenoid valves do have an unfortunate habit if sticking open on mains water. Some/many (bigger ones?) are diaphragm valves with a very small solenoid pilot valve. The only one I used on a very critical mains water supply stuck on at a very inconvenient moment. Washing machine valves seem to work OK, mostly. I'd probably supply your system through a PReducing Valve set at less than 3 bar (usual) operating pressure of the P Relief Valve.

[Ian Jackson]

In message , Ron Lowe writes

Although I never tried it, I have always understood that egg white was one of the olde tyme cures.

I did try mustard powder. Big mistake. Not only did it not work, but the car stank of mustard for months and months.

If I were you, I'd try one of Roger Mills's suggestions!

[Roger Mills]

It would need to be set to *considerably* less than 3 bar. Otherwise, if it cranks it up to nearly 3 bar when cold, it will over-pressure when hot.