John Rumm wrote:
On 18/12/2020 20:28, Chris French wrote:
So, fitted the new gas valve to the boiler and the house is warming up nicely
now.

I set the output pressure on gas valave (abiout 12 mbar), and while I was at
it
checked the supply pressure on the valve as well.

It was about 14-15 mbar. So somewhat low..

I checked the pressure at the meter, it was fine, 21 mb.

ISTR from that a quick look at the manual the other day, the input
pressure latitude was quite generous on that boiler. Probably helped by
not being fanned flue with forced combustion etc. So although likely
well out of spec it will probably work fine.


It does seem to have been working fine all these years. and I don't think is is
a new situation.

The bigger worry would be could the boiler firing momentarily extinguish
a burner on the hob? If so, does that have flame failure detection?

It doesn't (or at least if it supposed to it doesn't work) , which is a bit of
a concern, but then again it's never happened so far, and at one point we had a
gas oven as well (now electric).

Now this doesn't entirely surprise me. We have lived here since 2004, there
is
the boiler and the gas hob on the same pipe (they are on oppsite sides of a
wall), if the hob was on full, you would notice a change in the burner sound
when the boiler fired up. So I suspect it maybe has been like it for a long
time (we've never had aplumber in, it's never been checked). Everythign
wroked
ok, and doing anythign about the supply would be a PITA until we rdid the
kitchen and utility room area. so I let well alone .

A ssume this is down to the pipe run, most of it runs under the floor, the
total run is probbaly about 25m, the first 4m or so is 1inch OD steel pipe,
somewhere between there and the boiler/hob it tunrns into 15mm copper, there
are probably 4-5 bends on the way.

The boilers rated gas consumption (it's a basic open flued, on/off boiler) is
4m^3/hr.

so given that it has worked in this fashion for presumably some years I am
minded to carry on, we hopefully will get round to a full kitchen refit in
the
next few years.

what are the implications of that sort of low pressure?

As above, plus possibly lower than expected boiler output (although at
35kW+ you may not notice!)

The system seems to perform ok. it's a pretty large victorian house so needs
plenty of heat (hence 35Kw :-) ) and soem of the rads are undersized I think
(system probbaly installed in the 1970's, maybe eary 80's I think), though the
boiler was a more recent replacement. ISTR that a while back, after moving in I
did heat clacs for the rooms/house and overall the boiler was sized big enough
with spare capacity for the building)

You could always run through the calcs to see what the setup ought to be:

http://wiki.diyfaq.org.uk/index.php/Gas_pipe_sizing

It seems like it should be sufficient with a quick calc, goign on the table on
there.

It looks like most of the run is 1 inch steel pipe. maybe about 25m given the
likly route, though most hidden away under wooden and concrete floors.
Probably 7-8 elbows. Say an effective length of 30M, which should be able to
supply 5^3 m/hr. so plenty for the boiler. There is a bit of copper after that,
but only maybe a metre or so and a few elbows..

I may redo my measuremnts to check. but whilst everything works I'm not really
goign to do anything about it givem it wold presumably mean replacing some of
the gas pipe.

thanks

--

chris French