Boiler pressure zero but no visible leaks - please help!

SausageCat_2

I would be very grateful for advice.

I live in a rented first floor flat (managed by an estate agent). Around 2 months ago I bled a radiator in the bathroom, which led the boiler pressure to lower to zero and the boiler cut out. I put water in and the boiler kicked in. However, the pressure gradually went down and within 2 days it was almost zero. After that I had to keep putting water in every 2 days in order to keep the boiler going, so I contacted the agency and a plumber came.

He inspected all the radiators but there is no water leaks around pipes. There is also no water coming out of the outside pipe. And since the boiler pressure does not go up when the heating comes on, he concluded there must be a leak somewhere. We checked underneath kitchen cupboards (boiler is in the kitchen) for leakage but there was none.

Initially, as long as the heating was on, the pressure stayed up. Now even with heating on continuously the pressure goes down. I put water in in the morning to 1.5, within 3 hours the pressure is almost zero. The heating never comes on in the morning as the boiler had cut out during the night. In the last few days I had to turn the thermostat to the lowest so that the boiler doesn't try to fire up, making loud noises and waking me up.

The plumber says he can't do anything until a leak becomes visible. People downstairs say there is no leak on their ceiling. I would have thought that I would smell stale water if there was a leak, given the amount of water that went in the boiler.

I can hear the boiler is struggling even when it's on, and am worried that one day, possibly during Christmas, it won't start up. I'm wondering if there is another possible cause for this, and would really appreciate any suggestions.

Head_The_Ball

What type of boiler is it?

We have a Potterton Powermax HE which is fully enclosed in a metal casing. It is similar to this one.

We had a problem with falling pressure, although not as extreme or as rapid as yours.

Like you we could not find a leak anywhere in the pipework.

It transpired that the circulation pump, which is enclosed inside the metal casing, had a leak. There was sufficient heat to evaporate the leaking water before it dripped from the casing.

We only discovered the problem when a Potterton service technician opened up the casing to investigate.

The pump and the area around and below it had a lot of limescale build up left from the evaporation of many litres of water.

SausageCat_2

Thanks for your reply. That may be a possibility.

The boiler is called MAIN Combi 24 HE, and other than heating/hot water selector, heating and water temperature controls and pressure gauge, everything is enclosed. The same plumber did an annual service in May and opened the casing to check everything was fine. I do remember though, he topped up water as well, as the pressure was too low...

lewishardwick

You should have a pressure relief valve somewhere. That may well be leaking to the outside. Can be hard to spot from the outside if it's gradual.

SausageCat_2

The plumber dismissed it, as there was no visible leak from the outside pipe. I've put so much water in to the system, it would be visible if there was a leak wouldn't it anyway?

malky39

Has the expansion vessel been checked that it is pumped up to the right pressure or faulty

Lorian

malky39 wrote: »

Has the expansion vessel been checked that it is pumped up to the right pressure or faulty

^ seconded.

SausageCat_2

No it wasn't checked, and the plumber is so certain there is a leak that he doesn't want to do anything until a leak is visible. He said that because the pressure doesn't go up when the heating comes on, it isn't the expansion vessel that's causing the problem. Is this correct?

He's a chosen contractor by the agency and as I'm seeing someone from the agency tomorrow, I wanted to see if I had a good reason to ask for another plumber for second opinion. Now it seems there is, which is great!

eamon

I've got a different make of boiler but experienced similar for a few years. Had the expansion vessel topped up etc. To the OP are you seeing lots of steam (will be white in colour and not light grey these are exhaust gases) coming from the flue (outside). If you are then it is possible that the primary and or secondary heat exchanger is leaking water, dripping unto the burner immediately evaporating and exiting via the flue. This problem will cause a drop in water pressure. Its a lot trickier, more expensive and time consuming than refilling the expansion vessel or changing the PRV.
Hope that helps.

bris

The heat exchanger can leak and the water goes through the condensate trap so impossible to spot.


Where the condensate pipe goes into the boiler (white plastic 21.5MM) disconnect it from it's hose, pressurise the system and check for leakage.


Wait, the boiler is to old for that type of heat exchanger I think, but give it a try anyway..

Alex1983

There boiler doesn’t have that sort of heat exchange, it’s a conventional heat exchanger with a 2nd heat exchanger up by the fan.