Tracking down a central heating system leak

skotbites

Hi I know this is an old thread but I'm struggling with a similar problem (main combie 24 HE)

Fine during the summer hot water no problem. Come this time of year I'm having to top the system up every 2 days or so. Not been able to find any visible leaks around the valves etc.

Could this be the PRV? Or would that affect the hot water too?

Thanks

Edit: there's also no overflow pipe outside to check

SuzieSue

When we had this the plumber told us to check behind all the radiators for a leak. He was correct - one of the pipes in the wall behind the kitchen radiator was leaking. Unfortunately I didn't spot it until I noticed a large wet patch on the ceiling below (the kitchen is on the first floor).

bridgedino

The prv would be a likely candidate If the expansion vessel has lost its charge.

The pressure relief discharge pipe which should be external to the property would be wet/dripping once the system gets up to heating temperature

crazylady100

I would ring a Leak Detection company like the one we used (see previous post) and see if they can give you any advice over the phone before you start spending money on plumbers and heating engineers. They may be able to give you some pointers to check yourself or at least let you know if they think they could find your leak.

malc_b

What's not been mention on this thread is whether the pressure still drops if the boiler is left off. If the PRV (copper pipe venting outside) leaks when the system is pressurized but off then PRV is suspect. If the leak in PRV occurs only when the boiler is hot then the expansion vessel is suspect.


To explain, hot water expands. The job of the expansion vessel is take this expansion. In the EV is rubber ball or sheet. One side is air, the other water. The air must be at the cold pressure, typically 1bar. When the boiler heats up the excess water is forced into the EV and the pressure rises. If the EV is 33% filled then that would be to 2bar. PRVs are 3bar. If pressure rockets up when boiler heats up then EV is faulty, either air has gone so needs pumping up or it has a leak. Note you need to de-pressurize the water side before pumping up the EV. If the EV is gone then if the boiler stays cold the pressure should hold. When the boiler heats up the pressure rockets and the PRV vents. When the boiler is cold again the pressure has fallen due to the water lost through the PRV.


It's also possible to have a hot leaking PRV due to the EV being set too high (most come set to 1.5bar) or being undersized.

Henry-Root

I have a similar problem with a slow pressure drop with a new Vaillant Ecotec Pro 28.

Daft question but how did you find the leaks and where were they? Before I had this new boiler fitted we thought there was an underfloor pipe leak as two radiators required constant bleeding. All radiators work fine now except one upstairs which is a bit slow but we don't get any air in them at all now.

Any help much appreciated as I must have topped up the pressure about 6-10 times in the last 3 months. The plumber says it's not the boiler but that was some time ago.

I am also a little concerned about the use of leak sealer. Plumbers must have put about 3 lots in during the last 6 months but so far as I know Vaillant do not prohibit this. If anyone knows otherwise please let me know thanks. :A

Cisteria

I had the leak sealant put in and it worked a treat for about 3 months. On the plus side - we know the problem's in the CH system... On the down side... you see where I'm going with this.

Going to keep reading the threads... if anything, it's good to feel you're not alone. If there's someone out there that just LOVES to trace leaks in ground floor flats with concrete base and laminate flooring, please speak up... The regular CH / gas people just seem to lose interest at this stage.

Cisteria

Having had the boiler engineer in x 4 and thinking that options on the boiler were exhausted as it was only when the CH was running that pressure was lost (not hot water), I got UK Leak Detection in (expensive but extremely thorough).

After using three types of imaging equipment, UKLD didn't detect a leak BUT did detect that there were metal particles in the boiler's condensate trap from the CH heat exchanger. The suggested problem is a crack in the CH heat exchanger allowing central heating water to pass through into the exchanger with debris, hence the rapid loss of pressure but ONLY when the CH is running. (I hadn't realised that the heat exchangers for water and CH are separate units). The heavy debris drops into the condensate trap, and any escaping water that's not captured by the condensate trap would be vapourised rapidly in the exhaust vent (also not previously checked for water vapour).

The leak detection engineer checked the condensate trap at the end of the survey as he'd come across this problem with a customer earlier in the year. On both occasions the UKLD engineer was surprised the boiler man had not checked this first so it's quite possible yours hasn't either. Hope this might help if you still have a problem!

So now it looks like my 8 year old, regularly serviced Vaillant Ecotec boiler needs replacing, but at least we have an explanation.

I can also recommend UK Leak Detection. It is pricey but the engineer was here for 6 hours and didn't want to give up until he'd found a solution, even though the solution he found wasn't technically his area of expertise!