Just been round to our (non-technical) friends.

They have recently ( 6 months or so) bought a house which has an interesting
heating system.
The house had a loft conversion just before they bought it, which may have
resulted in a traditional gravity system being removed to clear the loft
space.

As far as I can tell they now have a spanky pressurised system with new hot
water store, pump, expansion vessels etc.
However the thermostat, programmer and boiler have not been replaced.

Now, they have been having problems, including a minor explosion which blew
the cover off the boiler so it dropped and partially blocked the flue
outlet.
They have had a plumber in who has fixed the boiler casing and said they
were very lucky not to be poisoned by the flue gasses.
The plumber also re-pressurised the central heating as it was not heating
the top floor.
Oh, and he told them that the heating wiring was all wrong and needed
sorting.
They are now also having another firm in to give a second opinion.

More interesting stuff - the boiler has a Warning label saying roughly that
the boiler is not suitable for use with a pressurised system because there
is no interlock.
Do not use, danger of explosion!
However a plumber has told them that it is now safe to use.

So they are very confused people (not surprisingly).
This leaves me with a number of questions/comments.

Firstly, the gas mini-explosion should have nothing to do with pressurised
or non-pressurised usage but is a strong indication that the boiler should
be viewed with deep suspicion and probably replaced.

Secondly, I am assuming that the boiler (an old Ideal IIRC) was originally
used with a gravity system but possibly not designed for use with a
pressurised system because it didn't have an interlock to prevent it running
if the system lost pressure.
This would explain the warning sticker from the person who serviced it late
last year.
If there was an explosion it would probably be due to heating a
depressurised system and generating steam in a sealed system.
I assume such a boiler could have a pressure sensitive switch wired into the
control circuit to provide an interlock, assuming the boiler was rated to
work at mains pressure.
This might cure the fault described on the label.

So if a boiler is labelled up as dangerous - do not use, then what is the
procedure for bringing it back into service after a repair?
Should a green label go over the red label?
A half hearted attempt has been made to remove the warning label but only
two corners have been removed.

This brings me to another issue.
The system is a pressurised system.
Now you can choose how often you have your gas boiler serviced but AIUI you
should have a pressurised hot water system safety checked every year.
Because I knew this, I knew to look for a label on the hot water tank which
said this.
However, unless you are a compulsive label reader, when you move into a
house with a pressurised hot water system if you haven't had one before you
are quite likely not to realise that there is a requirement for annual
inspection and maintenance.
Our friends had no idea that this was a requirement because they've never
had a PHW system before, just gravity then combi.
So new owners are very dependant on the previous owners to warn them about
the servicing requirements.
Seems like a safety loophole to me.

Having just been trawling through the Wiki on a related query, I could
pretend to be an expert ;-)

Cheers

Dave R

--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

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