Lack of Gravity fed pressure on non pumped heating circuit

We have 3 radiators fed by a non pumped gravity fed system linked to a back boiler on an oil fired AGA. The system was fitted a couple of years ago by someone who has now emigrated to NZ. The AGA is in a ground floor Kitchen and the 3 radiators on the first floor

The radiators are controlled by TRV's

Two of the radiators refused to work when switched on a couple of weeks ago - on investigating, I found that pipework feeding these radiators ran in the loft space and at one point ran over an old structural stone wall in a position higher than the feed and expansion tank ! - I raised the feed and expansion tank as much as possible so that it is now about 4 feet above the highest level of the associated pipework - got the two radiators working satisfactorily for about 4 days but now not working again.

I'm pretty sure that the whole problem is caused by a lack of gravitational pressure but can't position the F and E tank any higher - can anyone suggest a way of increasing the pressure without the installation of a pump? someone has mentioned installing a pressure vessel on pipework with a filling loop - is this an option if so where would this be positioned? Any suggestions appreciated[/b]

whodareswins said:

without the installation of a pump

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Why do you exclude the most normal and obvious solution?

Accessability to fit a pump - I'm presuming that since the installation was done by a plumber, he found the same problem hence not fitted originally- although having said that why did he fit the F and E tank below level of part of pipework run!!

pumps are most often fitted close to the boiler or the cylinder, but can be anywhere on the big pipe from the boiler before it start branching.

If you have a rising loop in the pipework it will tend to collect air or gas, and this will prevent gravity circulation.

Best approach would be to make a hole in the wall and run the pipe through flat. But a pump will push water over your loop and push the air forward until it can rise up and escape.

whodareswins said:

...why did he fit the F and E tank below level of part of pipework run!!

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I am just a householder and have not yet thought of a reply other than "because he's an idiot"