David WE Roberts wrote:
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.


not necessarily as you have seen later

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.

all sealed systems SHOULD have pressure relief safety valves. Not
necessarily part of the boiler at all.


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.


shrug.

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.

frankly its really overkill: ALL you have to do is make sure the
pressure relief system works

You have to have a stuck safety valve AND a stuck thermostat before the
tank will go up.


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.


*shrug* caveat emptor. First thing you do when gettigh a n old house is
have it looked over.


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

Cheers

Dave R



--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.