Hello everyone!

My problem is that I have a Worcester condensing combi boiler about 3 years
old that is behaving oddly. The pressure is fluctuating wildly.

When it is completely cold the pressure gauge falls to zero. The boiler still
starts though, and when it reaches its maximum working temperature the
pressure rises to nearly 3 bars, which is well above the green zone marked on
the pressure gauge.

I am getting it serviced in a couple of days by the firm that installed it
and they said they would 'look into' the pressure issue, but I wonder in the
mean time if anyone could suggest what may be wrong. I rather fear that the
firm I am dealing with may come up with some bull**** explanation -
especially since the boiler seems to be working perfectly satisfactorily
(except for the pressure readings).

--
Mike Lane (UK North Yorkshire)
To contact me replace invalid with mike underscore lane

Mike Lane wrote:

When it is completely cold the pressure gauge falls to zero. The boiler still
starts though, and when it reaches its maximum working temperature the
pressure rises to nearly 3 bars, which is well above the green zone marked on
the pressure gauge.

Classic case of loss of expansion space. The boiler contains an
expansion vessel that is charged with an air bubble. As the system heats
up and the water expands this is designed to allow the expansion y the
bubble compressing. If the air charge is lost, or the rubber diaphragm
that separates the air from the water fails, then you lose this
capability. The result is the pressure shoots right up until the
pressure relief valve opens and discharges some water (usually outside).
Once the system cools you end up with no pressure since you have lost
water.

For details on expansion vessels see the sealed system FAQ:

http://www.makewrite.demon.co.uk/SealedCH.html

As a temporary fix you can drain some water from a radiator so that it
is partially full of air. Don't bleed this out, and it will give some
makeshift expansion room.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/