"TheScullster" wrote in message
. uk...

"Grumps" wrote


We've got a 28 yr old Potterton conventional gas boiler serving a hot
water cylinder and 11 rads.
Over the past couple of weeks our old boiler has started boiling the
water. It has kettled for a few years, but this boiling is a new
development.
The British Gas man (we have maintenance on this old thing) said it was
most likely sludged up either in the HE or pipework around the boiler,
and thus the water is not circulating fast enough so it boils.
I thought we had a Y-plan system but can't seem to figure out the pipes
in the airing cupboard. I have posted a picture he
http://i56.tinypic.com/2vnj638.jpg
Physically the boiler is in the direction of the arrow shown.
"This looks like it comes from the boiler" is a pipe that goes to the
coil of the HW cylinder.
"This doesn't go to the boiler" is a pipe that doesn't appear to be in
the direction of said boiler and connects to the base of the pump.
I was expecting the hot from the boiler to go to the base of the pump!
I know it's difficult looking at just this one picture, but can anyone
explain if it is correct?
Ta.


Hi Grumps

Like you I would expect the boiler feed to be at the base of the pump.
The pipe heading towards the cylinder from the valve would be the central
heating feed.
The pipe heading away from the cylinder from the valve IYSWIM then tees
down (via some strange elbow arrangement) to the top cylinder connection;
and tees up to a reduced 15mm pipe - is this the cold water make up for
the heating circuit?
At this age it's likely to be vented with a loft header tank?
It would depend on the piping layout, but with our system (prior to
re-work) there was a serious build up of crud around a motorised valve and
at the vent/liquid interface. It could be that you have a similar issue
and the restricted vent is causing the boiler to pressurise a little.
Have you replaced any piping/valves to know the general
condition/cruddiness of the internals?
Have you kept a reasonable concentration of inhibitor in the system?
Have you ever flushed the system out (either chemical or power flush)?

Having had an old boiler replaced with a modern condensing jobbie, I would
hang on to the old girl as long as possible.
New models are far too complex for their own good IMHO.

Hi Phil

Ta for reply.

The strange elbow arrangement was my plumber's best attempt at fitting a
replacement cyclinder many years ago. The new couplings didn't line up with
the exiting pipework. The tee up to a 15mm pipe is for the bathroom rad
which is in the hot water circuit.

Yes, vented with a loft header tank.

The vent was coupled with the cold feed about 10 years ago due to another
blockage. So the cold feed is through the vent pipe. This, apparently, is
quite normal as a 'bodge' to give it some more years.

The system was drained but not power flushed about 4 years ago. The last
bits of water out were dark coloured. It was refilled and inhibitor added
then.

I'm sure people will have their opinions on the new(?) condensing units, but
have you reason to suspect that they'll not last as long?
According to Mr B.Gas, we'd save about £450 a year if we put in a new
A-rated boiler. According to my calculations, if my boiler can be brought
back to its peak performance of 65%, then a 91% efficient boiler would save
us £186/year. I think 91% is the max listed in sedbuk.
It'll take a good few years to recover the costs involved in a boiler
replacement, TRVs, flue re-positioning (it's too close to a window), etc.

Is it possible to just power flush the boiler and close-to pipes?