The last rad. in line does not get hot

[Boiler1]

Hi friends,

Im about to visit the site where the last (or few last)radiator(s) in the line does not get hot.
What would typically be the cause of that?
I was thinking of:
Air-lock (upstream)
Undersized pump
Undersized pipework
Short-circuit flow upstream

Is ther anything else that could cause this problem?

PS. If above were one pipe system, would some fault within the radiator be the cause?

 

[Cooky]

After you've eliminated air locks and water fouling (sludge in the water), I'd suspect the water is taking the path of least resistance through the radiators closest to the pump.

You can test this by shutting a couple of rad valves close to the pump, to see if the end-of-line rads get hot. If this works, you need to balance the complete hot water system.

 

[alanbalance]

Hi boiler, Assuming that the air and dirt is purged from the system, shut in the lock shields on the radiators closest to the pump to one turn or slightly less open. If the rads are hooked up to a single pipe system it will keep more flow in the loop increasing the loop resistance and encourage flow through the far rads. For a two pipe system shutting in the lockshield will cause more water to be available down stream of the ones close to the pump. Hope the rads have been piped up correctly.

regards alanbalance