Hello

I have Baxi back boiler that drives my hot water and central heating in a bungalow. The boiler is situated at floor level in the bungalow. The water is heated by an indirect coil in the water cylinder in the loft. There are two zone vavles.

The central heating system is fed from a water tank mounted high up near to the roof ridge in the loft.

The problem that I have is that this tank overflows when the heating circuit is working. I can hear and feel hot water running up a vent pipe that seems to run from the boiler that goes into the tank. And there is fluid coming out of the tank overflow pipe. This gradually dilutes the inhibitor in the system over time.

The guy who serviced the boiler tells me that he thinks that the boiler itself is working correctly.

I have been told by a friend that he thinks that the water level is just held too high up in the central heating tank and too near the overflow pipe, He has suggested that by fitting a new tank the water level could be held much lower than the overflow and this change will make the problem will go away.

The tank position is extremely difficult to get to let alone carry out any maintenance on it.

So I was thinking of replacing it with a tank mounted slightly lower and carrying out the changes in water level outlined above.

Is there any sort of limit to the height that I need to place this tank above either the hot water cylinder or the cold water tank?

No real limit although the header tank should be at least a third of the working head of the pump but not many people know that (except Scruff probably)!

As long as the pumps not in the loft you should be fine. The water level in the tank should only be two inches above the top of the outlet when the system is cold.

However if it's pumping over through the vent you may have a partial blockage around the point the feed and vent pipes join the system or the pump may be set too fast

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Sadly the pump is in the loft. Is there a minimum height that I need to have above the pump?

I'd say at least 1200mm although you may get away with a bit less with a decent pipe layout and air separator. Probably better to cut the pipework to the existing tank and fit a new ballvalve, adjusting it to the right depth before you put it back in the same place

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