Boiler losing pressure, need help finding the cause (leak?)

Bullit_2600

Hi

We moved into our house in 2021 which needed a bit of renovation work and we had a new Ideal logic max 30 kw combination boiler installed as well as some new plumbing work for radiators down stairs which required the pipes to be laid in the ground and concreted in.  The radiator pipes upstairs were not changed but there was other work to lay carpets etc.
Since moving in, whenever we have the heating on the boiler loses pressure.
We will set it to 2 bar and then within a few days to a week it will be well below 1 or at 0 and we have to top it up again. This has been happening for nearly 2 years now altho when the heating is off we don't have the issue so normally November to April we have to do this once or twice per week.#

The same plumber said that possibly the boiler couldn't cope with the load and we need an expansion vessel so we paid extra for that to be installed in November 2022. It hasnt fixed the issue.

In total we have 7 radiators downstairs and 6 up.  We have 1 bathroom with bath / shower, a cloackroom and 2 sinks in kitchen and utility room along with a water softener (in case any of this matters).

We cannot see any water leaks or damage anywhere which I thought we would especially if it was from under the floorboards and onto the ceiling - even tho it may seem like a small amount of water surely it would build up over 2 years of leaks?  Maybe it is in the ground or something else?

Not sure what options we have left other than getting some camera in to check for the leak which I was worried may be expensive so hoping to get some advice / guidance from one of you one here which would be greatly appreciated.

daveyjp

Easy things first.  Bleed every radiator and ensure the bleed screws are fully tightened.

A screw not tight by a fraction of a mm is enough for air to escape and the system to lose pressure.  That was the cause of our system losing pressure slowly, a bathroom towel rail which needed a fraction of a turn to tighten.

Bullit_2600

Cheers for the tip, I've recently bled them and have had to a number of ocassions.  I'll do it again and double check everything is tight. If they were leaking tho wouldnt there be water stains on the carpet/floor?

skycatcher

I had similar problem. Dodd every simple thing to remedy but ended up getting a leak detector company in....£300! They found it in 5 mins.... Under the concrete floor in our living room. They are were no signs of the leak but when a nearby skirting board was removed there was damp behind it! House insurance paid for the restorative work to be done.

JGB1955

We've had to 'top up' our system innumerable times... then the plumber tightened the valve on the only downstairs radiator without a TRV and ... magic!  It had probably been leaking for 3 to 4 years but, being on a concrete floor, no damage!

mi-key

Mine did the same for a few years, and needed topping up every month or so. Eventually found a pin hole leak in a pipe where it passed through an internal wall ! because it was leaking so slowly, the bricks were soaking it up then drying out

locky123

Checked the pressure relief valve isnt dripping from the discharge pipe?  Checked the expansion vessel is holding the correct pressure? Cracked heat exchanger?

locky123

How high does the pressure gauge get and how quickly after the central heating has been on for 30 mins, after it was immediately topped up?

ThisIsWeird

I suspect Locky is on the case, Bullit.

For a start, tho', a 2bar cold pressure is too high - top up only to 1 or 1.2bar. Then monitor what happens to the pressure when the boiler is turned on from cold, and for say an hour until the rads are piping. Please report back.

At the same time, locate the safety discharge pipe going outside your house from the boiler - it'll likely be on the nearest wall to the boiler. It'll be 15mm copper, and either point down close to the ground, or will bend back on itself and point against the wall. When you find it, tie or tape a small clear plastic bag over the end to monitor any discharge - there should be none.

Try that as the obvious first step, then we can try other things like isolating the rads and pipes (easy) to determine whether the loss is within or without the actual boiler.

ThisIsWeird

And, the inhibitor content of the system water will now be insignificant, and you'll be running the risk of system corrosion. Once you ID and sort the issue, make sure fresh inhib is added.

SonofMaurice

I'm no expert but 2 bar sounds quite high to be setting the pressure at. Most boilers should be at 1-1.5 bar, are you sure it isn't venting through the pressure relief valve?

We recently had a similar problem which turned out to have a bizarre source - a radiator thermostat had cracked at the base (probably knocked or something) and, unnoticed, was sitting slightly skew on the valve pin. This must have caused enough lateral pressure on the pin when it was operating to cause the seal to weep. As the radiator was over a suspended floor the small amount of water either evaporated or made it's way under the house. I found it by tying a loop of paper (toilet paper is best) under the joints on all the radiator pipes. While the water may go, the paper will distort or dissolve enough if it gets damp for you to spot a leak has happened.

If the simple suggestions don't work then a leak detection company may be the only (expensive) route to go. Apart from being a pain to keep pressurised you don't know if it is causing any damage to your home or boiler/CH system that could end up being a lot more expensive in the long run.