Several years ago I had a wall-mounted boiler fitted to replace an old
floor mounted one. The subsequent re-organisation of the plumbing has
caused a number of problems since, including the production of
'interesting' sounds from the CH system at various points in the
heating cycle.

A couple of years ago I noticed, when preparing to drain and flush the
system, some clumps of nasty brown growth floating in the CH header
tank. Thuis has been observed to re-appear at regular intervals.
This phenomena I think is the result of the configuration of the pipe-
work, in that, at the end of the heating cycle, when the boiler and
pump switch off, I've detected hot water going up the cold-water feed
into the header tank, rather than via the expansion/ overflow pipe. I
have recently felt this [hot] backfeed by putting my hand in the
header tank over the outlet to the boiler.
I'm thinking that this has to do with the reduced 'rise' of the
expansion/ overflow pipe coupled with a more powerful convection-
upflow from the boiler.

It occurred to me that I might use a one-way valve device, which I
discovered recently is known as a 'check valve' thus taking away the
easier route for the hot water backfeed and hopefully reduce the
amount of hot water getting back into the tank, although I think some
may still get in via the overflow pipe].

My questions are these:
[1] How likely is it that fitting a check valve be successful in
stopping the hot water back-feeding up the inlet pipe, and
[2] What's the best orientation to fit check-valve, horizontal or
vertical ? [there's space for either and I suspect the vertical
orientation will work best].

TIA

On Wed, 05 Dec 2007 01:42:34 -0800, Catweazel wrote:

A couple of years ago I noticed, when preparing to drain and flush the
system, some clumps of nasty brown growth floating in the CH header
tank. Thuis has been observed to re-appear at regular intervals.
This phenomena I think is the result of the configuration of the pipe-
work, in that, at the end of the heating cycle, when the boiler and
pump switch off, I've detected hot water going up the cold-water feed
into the header tank, rather than via the expansion/ overflow pipe. I
have recently felt this [hot] backfeed by putting my hand in the
header tank over the outlet to the boiler.
I'm thinking that this has to do with the reduced 'rise' of the
expansion/ overflow pipe coupled with a more powerful convection-
upflow from the boiler.

Convection involves a circulation which isn't occurring in this case since
there isn't a return path. It sounds as if it's expansion of the system
water that's occurring, and if you put a check valve in there then it's
liable to go up by the vent pipe instead.

A normal spring check valve also requires a significant head to overcome
the resistance of the spring so your system is likely not to fill properly.

I suggest you clean the muck out of the header tank, disinfect it with
bleach or maybe Jeye's fluid and refill it adding maybe an inhibitor with
a biocide.

--
John Stumbles

My karma ran over my dogma

In article ,
Catweazel writes:

Several years ago I had a wall-mounted boiler fitted to replace an old
floor mounted one. The subsequent re-organisation of the plumbing has
caused a number of problems since, including the production of
'interesting' sounds from the CH system at various points in the
heating cycle.

A couple of years ago I noticed, when preparing to drain and flush the
system, some clumps of nasty brown growth floating in the CH header
tank. Thuis has been observed to re-appear at regular intervals.
This phenomena I think is the result of the configuration of the pipe-
work, in that, at the end of the heating cycle, when the boiler and
pump switch off, I've detected hot water going up the cold-water feed
into the header tank, rather than via the expansion/ overflow pipe. I
have recently felt this [hot] backfeed by putting my hand in the
header tank over the outlet to the boiler.
I'm thinking that this has to do with the reduced 'rise' of the
expansion/ overflow pipe coupled with a more powerful convection-
upflow from the boiler.

It occurred to me that I might use a one-way valve device, which I
discovered recently is known as a 'check valve' thus taking away the
easier route for the hot water backfeed and hopefully reduce the
amount of hot water getting back into the tank, although I think some
may still get in via the overflow pipe].

Hang on a mo...
That tank is there in order to accomodate expansion of the
water in the heating system as it warms up. You therefore
expect that warm water will enter the tank from the bottom
in normal operation.

Is the tank covered? Could the brown growth be the remains
of a bird or squirrel or mouse? It sounds like the system
might be in need of a drain down and flush through, and
refill with inhibitor.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Wed, 5 Dec 2007 01:42:34 -0800 (PST) someone who may be Catweazel
wrote this:-

This phenomena I think is the result of the configuration of the pipe-
work, in that, at the end of the heating cycle, when the boiler and
pump switch off, I've detected hot water going up the cold-water feed
into the header tank, rather than via the expansion/ overflow pipe.

You don't have a cold water feed pipe. What you do have is a feed &
expansion pipe. This allows water to flow into and out of the
heating system when necessary. When the heating is turned on and the
water in the system expands it flows up the feed & expansion pipe
back into the tank. When the heating is turned off water flows back
down the f&e pipe as the water in the system contracts. This is
dependent on the water temperature, if it really only happens when
the pump is turned off then there is a problem with the pipework
design.

You also have a vent pipe. This is there as a safety feature, if the
f&e pipe is blocked then this will allow the water to
expand/contract without causing an explosion or collapse.

It occurred to me that I might use a one-way valve device, which I
discovered recently is known as a 'check valve' thus taking away the
easier route for the hot water backfeed and hopefully reduce the
amount of hot water getting back into the tank, although I think some
may still get in via the overflow pipe].

Don't be a fool.

My questions are these:
[1] How likely is it that fitting a check valve be successful in
stopping the hot water back-feeding up the inlet pipe, and

Probably 100%. What then happens depends on how lucky you are. If
you are lucky you may get away with it for a while. If you are
unlucky some part of the heating system will explode, probably a hot
water cylinder.




--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54