Mismatched zones

[lostdirection]

Bit of advice really, although I suspect theres not a great deal I can do about it.

We have 2 zones, 1 that covers most the house radiators the other zones covers the big radiator in the loft conversion.
The 2nd zone I think was needed for building control.
Its a new oil boiler.
The issue is that when the 2nd zone fires up the boiler, its return feed is very quickly back to the boiler which switches it off due to the temperature.
The radiator though is mostly stone cold. This cycling continues.
The main zone works fine

Short of joining the 2 zones together can I do any tricks?

 

[John.g]

TBOE was the original (and best?) and is still used in some installations, until somebody discovered that BOE works just as well, it still amazes me that when you admit hot water to a (BOE) rad how it immediately rises to the top and then flows downwards, very like the TBOE.

I don't know if air builds up in a tight rad, judging by mine, it may do eventually but anytime I open my attic vent rad there is a very slight vacuum in there so perhaps has to be some air there? but the rad runs perfectly satisfactorily for months/years on end in this manner. I do have get rid of all the air initially and then it runs away fine.
I just checked it now with the L/shield just cracked open to keep the rad full and it is practically cold, as soon as reopened the L/shield fully, rad back to normal.

 

[Ric2013]

Hi John,
I must admit you lost me in previous threads. Is your point that your loft rad only fills by virtue of pump pressure as it is lower than your F&E cistern and you suspect the OP has the same problem?

 

[John.g]

The top of my rad is ~ 0.5M above the attic floor and the water level in the F&E tank is ~ 1.5M above the floor level so no problem in filling the rad, its only with the circ pump on that the "vacuum" appears, a circ pump head (pressure) is the differential head between the suction and discharge, a pump with a 3M head could have a suction head of -1M and a discharge head of 2M with a open system due to pipe losses and any rad high up (like in the attic) can have negative pressure with the circ pump on.
The F&E tank is normally sitting on the attic floor with its level only slightly higher than the rad top but the rad should still fill with the pump off, don't know the OPs set up with the pump off.

 

[Ric2013]

I don't get why a 2-zone system should be a problem as such: I designed a system for my mother's house that had 5 heating zones, each controlling a single radiator and it didn't have this problem.