Low system boiler pressure Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[moselinf]

We have recently (September) had or whole central heating and hot water system replaced from an open vented system to an unvented system with condensing boiler (pressurised to 1.4 bar).

All worked satisfactorily until 2 weeks ago, the boiler went into fault due to low system pressure (0.4 bar). The bolier manufacturers have visited site and could not find a fault with the system, but replaced the pressure safety valve as a precaution. However the probelm has re-occurred. I have check for obvious leaks in the system, but found nothing.

We are now having to re-pressurise the system on a daily basis. The real problem is that the downstairs central heating pipes are buried in a solid floor, has anyone any suggestions of how I might be able to identify and locate a leak within the system without having to rip the entire house apart.

[ALDA]

WITH THE BOILER LOOSING PRESSURE EVERY DAY, THIS EQUATES TO A LOT OF WATER! (1-2 LITRES/DAY).

LEAK CAN’T BE ON FIRST FLOOR! (WATER WOULD BE DRIPPING FROM CEILINGS).

SO SEARCH GROUND FLOOR, TAKE UP FLOOR COVERINGS.

CONCRETE IS POROUS SO WATER MAY HAVE FOUND ITS WAY TO SURFACE. LOOK FOR OBVIOUS SIGNS (DAMP PATCHES) THAT MIGHT INDICATE LEAK IN A PARTICULAR AREA.


I WOULD SAY IT WOULD BE A POOR INSTALLATION IF THERE WERE JOINTED PIPE RUNS BURIED IN THE CONCRETE (THEY SHOULD BE CONTINIOUS). SO HOPEFULY (IF THERE IS A LEAK) IT WILL BE WHERE A PIPE COMES OUT OF THE FLOOR TO THE RADS, WHERE WITH CONSTANT MOVEMENT THROUGH EXPANSION/CONTRACTION ETC A CRACK COULD HAVE DEVELOPED IN PIPE, NEAR OR SLIGHTLY BELOW THE SURFACE.

IF NOTHING IS REVEALED, IN MY OPINION ONLY, YOU COULD TRY:

1). CARRY THIS OUT WITH BOILER SWITCHED OFF AND ALLOW TO COOL DOWN.
2). CLOSE ALL GROUND FLOOR RADS (FLOW AND RETURN) LOGGING NUMBER OF TURNS SO THAT THEY CAN BE REPOSITIONED TO BALANCE SYSTEM LATER.
3). NOTE SYSTEM PRESSURE (IS IT FALLING AND HOW FAST)
4). OPEN ONE GROUND FLOOR RAD AND NOTE IF THE ADDITIONAL WEIGHT OF WATER INCREASES THE SPEED AT WHICH THE PRESSURE FALLS.
5). REPEAT STEP 4. WITH A DIFFERENT RAD UNTIL YOU HAVE GONE THROUGH PROCESS FOR EACH OF YOUR GROUND FLOOR RADS.
NOTE IF ANY CHANGES IN RATE OF FALLING PRESSURE IS SIGNIFICANT FOR A PARTICULAR RAD AND THEREFORE THE PIPEWORK INVOLVED.
NOTE: ONLY OPEN ONE RAD AT A TIME (CLOSE PREVIOUSLY OPENED RAD)

I CAN HEAR YOU SAYING THIS IS A LONG DRAWN OUT PROCESS. "CANT GUARANTEE IT WILL WORK" BUT IT MIGHT JUST GIVE YOU AN IDEA OF WHICH PIPES ARE LEAKING AND WHAT HAS TO BE DONE TO UNCOVER THE AREA INVOLVED.

BEST OF LUCK.

[htg engineer]

Check pressure doesn't rise when the heating is on, check pressure relief discharge for leaks. Is there anywhere you could blank the pipework before it enters the concrete - then see if the pressure still drops. (if it doesn't drop you know the leak is under the concrete)

[Sparkgap]

Shut off underfloor heating and check pressure loss. Open one circuit at a time and check again, that will tell you if you have a problem with the underfloor part.
Also check expansion vessel. The air pressure in mine dropped and when water expanded some was forced out through safety valve to outside and I kept having to top it up until I found the cause.

[moselinf]

Thanks for the advice, we'll give it a go.

[roger196]

Worth checking concrete floor with damp meter. If you do not have one, use a multimeter to measure resistance of floor with probes held about one inch apart. You will need to hold this distance constant using holes drilled in a piece of wood or other insulating material.
A damp floor has a lower resistance than a dry one.

[moselinf]

A friend suspects that as we can see no evidence of a leak (yet!), the system may be losing water through a number of tiny leaks rather than one large one. And he suggests the use of an internal leak sealant (e.g fernox F4) which is compatible with a pressurised system and can be dosed via the radiator bleed valves.

What are peoples thoughts, how 'long term' would this fix be?

[ALDA]

M,

THIS WILL BE A SHORT TERM TEMPORARY SOLUTION AT BEST ULTIMATELY JUST PROLONGING THE INEVITABLE AND THE AGONY.

IF THE PIPES ARE CORRODING AS SEEMS TO BE THE GENERAL CONCENSUS, I WOULD ADVISE YOU BITE THE BULLET AND RESOLVE THE SITUATION SOONER RATHER THAN LATER AS THE CONDITION OF THE PIPEWORK WILL DETERIORATE FASTER AS TIME GOES BY REGARDLESS.

HAVE YOU CONSIDERED ISOLATING THE GROUND FLOOR SECTIONS OF OLD FLOW AND RETURN PIPES AND RE-PIPING ABOVE FLOOR LEVEL TO YOUR RADS?

SAVE TIME AND A LOT OF HEARTACHE!

IF YOU USE MICROBORE AND MAKE VERY TIDY JOB OF INSTALLATION THE APPEARANCE WILL BE VERY ACCEPTABLE OR YOU COULD EVEN CONCEAL BEHIND HOLLOW BACKED SKIRTING/CLADDING.

CHIN UP. KIND REGARDS. ALDA.

[Oliver_murphy]

I woudnt of thought you have a leak, on a pressurised system, even the minutest of leaks would drain your system pressure VERY quickly.


When your system is next at 0Bar, fill it up to exactly 1 bar. Turn on your HEATING. Watch the gauge, if it rises more than 0.5Bar, then your expansion vessel has deflated.

Almost garantee this is your fault :D :D :D

[moselinf]

Thanks for everyones advise.

The leak finally surfaced at the weekend - a fault on part of the new installation and nothing to do with the existing pipework.

Pipework replace and system holding pressure.