We live in a converted barn with 15 radiators all at the same level apart from one and the system is an oil fired system. Boiler is old but regularly serviced. Only 5 radiators are now heating and will feed on gravity with the pump off. We have fitted a new pump after having the system flushed with a power flusher. Still only 5 radiators heating the rest are completely cold. They have all been bled following the power flush and new pump. Header tank not dry. Any Ideas
I presume when you say all rads have been bled that you actually got water from the aircock.
Have you got thermostatic radiator valves on all these rads?
If you have they could be sticking. (They often do after a few years).
Open them up fully to number 5 or 6 (as far as they will go).
Undo the nut holding the thermostatic head on. From the underside this is anticlockwise.
Now you will see exposed the valve linkage piston. This should go in and out with slight pressure -it works against a spring. (Use pliers to lift it and the side of a screwdriver to depress it, it's a bit too stiff for your finger).
You may need to apply some penetrating oil. When it's working freely without sticking you can re-assemble the valve. It should now be working.
But you didn't say if any of the rads have been working before.
Let's assume not since you took over the property.
Then you have a problem to identify the blockage. You will need to trace the piperuns back to where it is getting warm. This will probably mean exposing some pipework that is boxed in or below floors.
Even though there may be no positive circulation in a pair of mains, the flow pipe will warm up after the system has been on for some time. However after a blockage the pipe will be cold.
Having identified the position of the blockage there is no alternative to draining the system and cutting out a section of the pipe at that point. Take out 18inches either side of the blockage. Confirm what the obstruction is. (I once found a milk-bottle in a pipe). Then replace with a new section of pipe. Job done.
A note of caution here. Blockages are usually in the flow pipe as they are driven along by the pressure until it reaches an elbow or tee. All the above applies. If, however, the blockage is in the return it will be impossible to determine exactly where it is, although the above rules apply to a lesser extent. In this case a larger section of pipe will need to be removed. On the other hand you say the rads do not even get warm so it is most likely the blockage is in the flow pipe.
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