thanks for the reply, I thought that the coil may be blocked (faulty cylinder or something) but have forced water (with a hose) round the coil and it flows just fine. Also checked all connections on the cylinder for blockages, nothing there...
just tried another idea somone gave me which was to force water down the cold feed from the header tank.
This water went around the system and back out of the breather pipe back into the header tank, so guessing no-air?
Suggestion from someone might be that the gravity system might not work because of the new cylinder having more coils inside. I think the new cylinder has 2 more coils than the old one.
Could this extra water in the system, plus the fact that the connections to the old cylinder was badly scaled up so ruducing the amount of water flow cause the problem?
Sorry - didn't realise there was a page 2 - had already typed the following so thought I'd leave it>>
then:
Remove a radiator, connect hoses to each valve, one to garden tap and one to drain. Temporarily cut &cap feed, and cap vent. Turn on garden tap. Watch colour of waste water.
I did more or less this today - the water ran solid black/brown for about a minute! (Old cylinder in this case too)
Or you could hire a power flusher and make a day of it doing the whole system.
Or you could fit a pump to the pipes to the cylinder - pump when cylinder cool and pipe hot (2 stats)
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local