Gravity hot water not circulating please help

[gasmannn]

I had a problem with no hot water on a gravity circulation system, I thought the coil was blocked as it was getting hot to one side, so I changed the cylinder, still didn't work, I then found a two port valve boxed in and the head was gone so I replaced, started to fire but still hot to only one side of the coil, tried back filling through the boiler drain off got some heat round the return while filling with boiler running but once I stopped and tried running it again still won't circulate????

 

[Billy Bob Bob]

Thanks everybody that tried to help me and for all the advice, I made the flow to the coil about four inches higher than level. Once I filled up again this still didnt do anything, I called the manufacturer and asked if I needed a special cylinder they said I do cus the coil is not stretched for gravity and that's why it wasn't working. I was preparing myself to lay out for a new cylinder. I left the job and got a call a few hours later and they had hot water I couldn't believe it and now it's been a few days and had no call backs. It can only of been air and the restriction of the coil and eventually it just started circulating. I might not of made any money but I learnt a lot from this job, and if I go to gravity next time I will hopefully know the install as I think between us all we covered every problem that could exist on this system lol thank you all once again that was my first post and nice to know so many people are happy to help out

glad its sorted,its a headache and a ball twitcher when it goes pear,just remember nothing is ever strait forward with old systems so quote accordingly and explain why it might cost x because but if it does not etc

 

[gasmannn]

Will do next time gasman thanks

 

[oldhand]

I've successfully used this type of cylinder on a gravity system. The problem seems to be that the coils are almost horizontal and tend to trap air. Get the air out and it works perfectly well.

 

[sammathias]

Should never have a motorized valve on gravity??? also they recommend a cylinder with a coil that actually dips in the center to remove airlocks, however a standard cylinder piped up correctly should remove any airlocks!