Oil fired combi cutting out

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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?
How do you calculate the negative bar? That'll impress the engineer when he turns up this week.
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?
When the CH does get going without the boiler cutting out, the rads can be "too hot to 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.
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.
Replace the _ _ _ with @ . . and remove the ".hotmail.com" for a personal response which would be much appreciated.
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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

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.

Most definitely - take a look at approved document L.

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.

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

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
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