"Charlie" wrote in message
om...
In link
http://groups.google.co.uk/groups?hl...p%253Duk.d-i-y



I have a grants 90btu MKII oil fired combi which cuts out regularly.
It has the oil tank in the basement and the burner on the ground floor
I would say approx 2m above the bottom of the boiler. I believe it has
a two pipe tiger loop setup. Is that distance likely to cause the
negative pressure to be greater than 0.4 bar?

Its either a two pipe system with suction flow and excess return pipes back
to the tank from the burner pump OR its a single pipe to the tiger loop
device. I'm not sure what you mean by the burner is approx 2m above the
bottom of the boiler - do you mean oil tank?
10metres is the water head to give -1bar and greater height for the lighter
fluid. Unless you have a very long run of small bore pipe its unlikely the
suction losses will give a problem.
BTW what fireproofing is present for the basement tank as it sounds as
though its within the dwelling and must have 3hour fire resistant enclosure
(not an easy exercise to comply with)

From your comment about the burner cutting out regularly - is there a
pattern such as locking out after standing idle for a period such as
overnight? This is often down to a small air leak on the oil line which
allows the oil to drain back down and when the burner tries to start up it
has to first of all draw oil up the pipe and it locks out when it tries to
burn air. When reset it achieves a full suction pipe and fires at the second
attempt

How do you calculate the negative bar? That'll impress the engineer
when he turns up this week.

I doubt it - he'll probably just stick a suction gauge on the inlet pump
test point if he's in any doubt at all. If you want to work it out you need
to know the length of pipe, number of bends, internal diameter of the pipe,
coefficient of friction etc etc.


As well as the above the system has no thermostats other than the
stats in the boiler itself. no room stats, no frost stat, no rad
stats. I thought that would be a fairly standard setup these days -
are there building regs regarding use of stats in new build houses?

Most definitely - take a look at approved document L.


When the CH does get going without the boiler cutting out, the rads
can be "too hot to touch".

Have you tried turning the boiler CH stat down a bit? Mind you its probably
a limited movement stat which won't go below 65 degrees to prevent internal
"back end corrosion" of the shell. This will still be very hot to the touch.


The boiler is one of these with an internal 40 litre tank which is
kept hot so that there is DHW on demand. But at nighttime the echo of
the boiler can be heard in an adjoining bedroom. Would it be ok to
connect an external timer so the system is off totally between say
10.30 pm and 6am in the morning. Presumably this would mean bypassing
the internal timer which is one of those "lug in for on" and "lug out
for off" jobbies.

Worcester Oil combis do exactly that so I can't forsee that it would be a
problem, however you should ask Grant for confirmation of this

One other point which I hadn't considered was air in the system. What
is the correct procedure for bleeding a combi system? I always worry
about putting too much pressure in the system.

A Service Engineer who has worked on these boilers for 20 years is
hopefully coming out next week. What sort a questions should I be
asking him? The builder is prepared to pay the bill "if it isn't too
much". But as far as I can see this is a poor standard of
installation, with the possibility that the boiler is faulty as well -
there is a smell of fumes in the utility room - which has no
ventilation other than the flue of the boiler itself.

You havent actually said as much but is this a new house with a new boiler?
If it is then when was the build started since it perhaps should comply with
building regs. Certainly it should be properly commissioned by an OFTEC
registered engineer if you expect Grant to guarantee it. Having "worked on
these boilers" for twenty years suggests to me your guy MAY not be
conversant with a new boiler and I should ask for his credentials before
letting him loose on it. Grant will be able to put you in contact with a
competent oil technician or take a look at the OFTEC website and find a
local registered technician who can commission it properly for you.

John