Lack of Gravity fed pressure on non pumped heating circuit

[whodareswins]

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]

 

[JohnD]

without the installation of a pump

Why do you exclude the most normal and obvious solution?

 

[whodareswins]

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!!

 

[JohnD]

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.

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

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