why do my radiators always need bleeding

Unfortunately, there are several different types of indirect system and without knowing which type it is, there is only so far we can go with advice. If there is air constantly being drawn into the system, fitting a bigger pump may exacerbate the problem. If radiators are cold at the bottom and hot at the top, this is caused by insufficient flow of hot water. So if you have a new bigger pump, and still no circulation of water, where is it going? Well, there are several options. Firstly, is all the water circulating just some of the rads and failing to reach others?


Try balancing the system (See projects section on how to do this). Secondly, and probably more likely, a bypass valve has been left fully open, or the cylinder lockshield vale is fully open. So the water is simply taking the easiest route and avoiding the heating circuit. You need to google sundial plans (honeywell is a good site) and describe which plan is closest to your design. As for the valve, well that's how they break. Just turn, and nothing happens. It could be shut, open or in between. Trouble is, without knowing exactly where it is in the system, it is difficult to tell what it is supposed to do.


It may need adjusting, so does need to be replaced. Symptoms of a faulty cylinder are discoloured hot water from the taps, and overflowing central heating header tank. (The tank overflow to outside not the expansion pipe) AS you have not mentioned either, I would not point the finger at a fault here. Cold rads does not indicate a cylinder fault either. It took a day to change a pump (unnecessary? ), fiddle about and come to a suspect decision? Frankly, I would be wary. As I said though, I cannot condemn anyone as I cannot see the system.
I'm getting the impression that it's an open system with a header tank in the loft and not a sealed system where you top up the pressure via a filling loop?


If the latter then it won't be pulling air in through the vent. If you do have a vent, you could put your hand over it to see if it's sucking while the boiler is firing. To check if it's hydrogen and not air, when bleeding a radiator, put a match near the gas coming out of the bleed vent. If it lights then it is hydrogen which would point at sludge deposits/ rust being the problem.

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