Valve or Actuator at fault?

25 Aug 2007
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United Kingdom
Hi all

I've got a bit of a problem with our central heating. It comes on all the time that the hot water is on. I've narrowed the problem down to the 3 way value (a Danfoss HSA3). I removed the actuator from the valve and turned the hot water and central heating on and off and the actuator moved to the positions I expected.

I re-attached the actuator to the valve and did the same test, but it didn't move, but it sounded like it was trying to.

Now, I know that everything else is fine as the actuator does what I expected it to, but it appears that it doesn't have the necessary umph to turn the valve itself. Two possible thoughts:

The actuator is on the way out, doesn't have enough power to turn the valve. Solution is to replace the actuator.

The valve is too sticky and this means that the actuator can't turn it.

Can anyone tell me if I should be able to turn the valve by hand. It's quite stiff, and I need to use a pair of gas pliers to turn it. Is this too stiff and this is the cause of the problem, or is this normal for this valve?


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Usually something coming on when it shouldn't is the valve body sticking. Something not coming on unless the other is working is usually the actuator.
I would say that a 4" spanner and two fingers should be very easy to move the valve spindle.

You MIGHT just be able to free it up with WD40 but do NOT use any oil of any kind.

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Hi Guys

Thanks for the quick replies. I'll replace the valve asap.

- reliability of motorised valves is (overall) not bad
- reliability of the motors in the actuators is disgraceful!
- it's usually worth replacing (if possible) the motor in an actuator when it fails and everything else looks in good condition.
- it's hardly ever worth replacing the whole actuator and not the valve body. The price difference between head and whole valve is small, anyway.
- be VERY careful that you get the correct replacement valve. Apart from the obvious (2-port zone valve, 3-port valve), there are also multiple types of each: normally-open, normally-closed, mid-position 3-port, the 'other kind' of 3-port which has one port closed 'at rest', spring-return, motor-open/motor-close, low-voltage / mains voltage).
The Honeywell valves ALWAYS have type numbers on the actuator casing

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