potterton?danfoss clicking noise? help

[bridge9]

hi i have a potterton suprima 70l. which is working fine but for the last week or so it has started making a clicking noise. the noise is comming from one of the two white danfoss HP2A units which are on the pipes comming from the top of the boiler.? any help would be great.
i dont know what these danfoss units are or what they do but they have little leavers on them with two options, MAN and AUTO. they are on AUTO but when you put the one thats clicking on to MAN the clicking stops?
i leave them on AUTO because thats the way they have been since fitting!
thanks again for any help.
oh the pressure gauge is at 2 bar it thats any help?

 

[stem]

They are motorised valves. It's usual to have two, one for the central heating and one for the hot water, they shut the pipes off when the hot water or heating are no longer required.

The valves contain a small motor that when the valve should be opened is turned on, it winds the valve open and then 'stalls' but remains energised to keep it open. When the valve needs to close, the power to the motor is switched off and a spring pulls the valve shut.

I suspect that one of the valves is broken and instead of 'stalling' when it's open, it is slipping a cog. It's time for a new one, before it fails completely.

To find out which one it is, when you hear the clicking, switch off the central heating, and hot water at your programmer one at a time and the clicking will stop accordingly.

The motor part (known as the actuator) can be replaced without having to touch the plumbing. It's not a major job, an average DIYer should be able to change the actuator in a few minutes.

They should be on 'AUTO' the 'MAN' position keeps them open permanently and is used when filling & draining the system.

You can get one here or from most plumbers merchants

 

[bridge9]

hi stem thanks for the quick reply! and thanks for the info now i know what they are it makes sence to me. i know which one is making the noise as i can clearly hear it and i can feel it clicking when i put my hand on it. i'll pick up a new one over the next few days and replace it. i'm not bad with the old hands so it shouldn't be a problem. so thanks again and happy christmas.
thats the second time this forum has saved me hassle and money.
the first was my boiler locking out and some one said to resoilder the board and it worked fine!