Recomend a condensing boiler

stevem01

Poppycat wrote:

Thanks for the help guys. I have tried toppng up the system but pressue doesnt last long before it goes back to 0.

I ask another plumber for a quote, I dont think the one I asked can be arsed to send me a quote.

My combi used to do this - but it wasn't a water leak anywhere in the water pipes or inside the boiler that was causing it. It was because the air pressure in the water expansion vessel had reduced to virtually zero, due to leakage of the air from the expansion vessel.

Filling the system with more water simply caused the reduced volume of air in the expansion vessel to be pressurised into a very small volume. Then when the water in the boiler and pipework warmed up and expanded it caused the air pressure in the expansion vessel to increase by a large amount. As a result the water pressure in the boiler, pipework and radiators also increased to the same pressure as the air in the expansion vessel. When the water pressure reached the level where the over-pressure safety valve opened, some water was released from the pipework system, reducing the volume of water in the system and allowing the air pressure in the expansion vessel to reduce.

When the boiler was not operating the water in the system then cooled down and the pressure of the air in the expansion vessel (and the water in the system) was then lower.

The short-term solution was to locate the air valve on the expansion vessel and pump it up to increase the volume of air in the expansion vessel. This was pretty easy to do because the air valve was identical to the sort of valve used on a car tyre. Unfortunately, the air leakage from the expansion vessel still continued, so I eventually had to replace the expansion vessel, which wasn't cheap, but it cured the problem.

It might be that your problems are due to the same cause??

caveat_emptor

Poppycat wrote:

The pressue has dropped for months if not longer, but havent seen any leaks, although the downstairs piping is embeded in a concreate floor, which is lagged.

In my earlier post I forgot the most obvious place for a leak, and one that I've had, that is a leaky pressure relief valve. If the discharge is over a drain you could have a leak and not notice it. To check this out put a container under the discharge pipe.

Poppycat

Does the discharge pipe connect from boiler and go outside the house?

gromituk

Yes. A better thing to do is to tie a polythene bag over the end, so you can be sure that any water collected will definitely come from the heating system.

When you fill up the heating circuit, does the pressure very rapidly rise on the gauge, or does it rise steadily over several seconds as you introduce more water? And when you turn on the heating, does the pressure rise a lot more (from, say, 1 bar when cold to close to the 3 bar limit)? If so, it's pointing to pressure vessel faults, as described earlier.

Poppycat

Thanks gromituk I do what yu suggest tommorow as its too cold and dark outside now to get a bag attached to the pipe. Ist only a very small pipe if I recall correctly about 15mm in width and only goes out of brickwork about 2cm.

I just had to put pressue up as heating wasnt working due to fall in pressue. When I do fill it up it takes just over a sec to fill half way and so is quite quick.

gromituk

It sounds like your pressure vessel is kaput, as it's not absorbing water steadily like a balloon being filled up. This will most likely send the pressure up to 3 bar when the water heats up, so you lose water - the safety valve is only doing its job. If the pressure never gets up to 3 bar but you still lose water through the safety valve, it is faulty. Of course the gauge might be faulty too, but its needle is moving so it's probably OK.