Single feed indirect cylinders




Single feed indirect cylinders

		Single feed indirect cylinders commonly known as primatic cylinders were introduced and used widely until the mid 1970's. This type of cylinder keeps the water within the boiler and domestic hot water separate, overcoming lime scale problems and allowed pumped radiator circuits to be added.


	Separation of the primary heating circuit water and the domestic hot water is achieved by a plug of air trapped on initial filling of water within the heat exchanger inside the cylinder. One method of identifying this type of cylinder is by the absence of a smaller header tank that feeds the central heating system


Unfortunately, failure of the air bubble causes the central heating water, which is often discolored, to mix with the DHW, resulting in contamination. This could be caused by too much water on the central heating side, or by over pumping.This risk means that inhibitors cannot be used and this has therefore led to the use of indirect cylinders. Primatic's are no longer used and if you have one you may consider a replacement. It is not advisable to fit any type of pumped shower to this type of cylinder as the pump could cause the failure of the air bubble.