Honeywell V4073A mid position valve not moving: motor or PCB?

[jt12345]

Hi all.

I've got a Y-plan fully-pumped central heating system, but when the controller calls for CH, the synchron motor (in the Honeywell V4073A mid position valve) is not moving the valve round (and hence the boiler is not firing). I''m getting ~240V AC at both the white (CH ON) and grey (HW OFF) inputs, but (with the motor still connected) the "internal" feed to the motor (i.e the motor terminal which is *not* the blue neutral) is only showing ~63V AC. I've measured all these potentials using a (high-impedance) Fluke digital multimeter.

I'm assuming that this could be caused by either the motor burning out (which apparently they do regularly, due to the circuit design) or, alternatively, it could be due to something gone on the small pcb inside the head, next to the motor.

Could anyone please let me know if there is a way to tell whether I should change just the motor, or whether I should change the whole head? I've had the whole thing apart, so I'm happy to change either!

Many thanks, Jaime

 

[ProDave]

Does the actuator turn if detached from the valve body?

 

[jt12345]

Does the actuator turn if detached from the valve body?

My apologies - I've been calling the actuator the head.

Yes, it does. The whole system works perfectly for a day or two (including being able to select CH), then it seems to get stuck on DHW only i.e. selecting CH does nothing, and selecting CH+DHW only seems to make DHW work. I can temporarily "fix" the problem by moving the lever over at which points it all works perfectly again for another few hours. I've also removed the synchron motor from the actuator twice, and both times the motor has started working (i.e. connecting the motor to the mains supply makes it spin slowly). I've also tried (gently) turning the valve spindle by hand and it seems to turn freely, albeit through only about 15 to 20 degrees of rotation (I assume this is as intended!)

It's a classic intermittent problem - every time I strip it down, it starts working perfectly!

 

[ProDave]

So when you remove the actuator, does the valve turn freely by hand?

My guess is the mechanical bit of the valve is worn and sticking or stiff.

 

[jt12345]

So when you remove the actuator, does the valve turn freely by hand?

My guess is the mechanical bit of the valve is worn and sticking or stiff.

Yes, when I remove the actuator, I can turn the valve spindle freely by hand. I haven't measured the angle of rotation, but "off the cuff" I'd say it was only about 15 to 20 degrees - does this seem "correct" for one of these valves? (I'll grab the protractor and some adjustable pliers tomorrow to measure it more accurately).

 

[Rob_the_rich]

I think it should be 45 degrees, only thing I can find on the web is this article http://www.lovekin.net/honeywell-motorised-valve-faults.html which also mentions 70 degrees for a 2 port valve.

63V may well be correct, as an ac voltage is applied to keep the valve in the heating-only position, see http://www.diyfaq.org.uk/plumbing/controls/midpositionvalve.htm

Cant see any cpu in there, just a tranny, a couple of resistors and a couple of switches, although might be miniaturised.

So I would agree with Dave, valve mechanism getting stuck.

 

[Rob_the_rich]

oops, diode not tranny. :facepalm:

 

[jt12345]

Ok, I have a question for anyone who can interpret circuit diagrams. Looking at that internal schematic diagram           on the DIY FAQ page, am I correct in saying that:

*if*

1) I have ~240V AC on the white input (CH ON), *and*

2) I have ~240V AC on the grey/gray input (HW OFF), *and*

3) I have ~63V on the feed side of the motor (i.e. the other side of the motor to the blue neutral input),

*then*

4) microswitch 1 *must* be broken?

I think this is correct, but I am not a qualified electrician, so I would appreciate a confirmation from someone who knows. Thank you, Jaime

 

[ProDave]

Use your meter on the ohms range to check operation of the microswitch. With the power off of course.

You still haven't answered of it moves to the correct positions with the actuator head removed from the valve body.

 

[jt12345]

Ooops -   my bad!

 

[jt12345]

I *do* like this forum system, but it does take a little bit of "getting-used-to" at first!

Use your meter on the ohms range to check operation of the microswitch. With the power off of course.

Yes, I'm aware of that. But since moving or touching anything has "temporarily fixed" (irony alert!) the problem twice already, I'm inclined to just spot-probe potentials/voltages if that provides me with the same info (and it should do!) Another issue with removing the power and using the meter on the ohms range is that there is of course the parallel circuit through the diode, switch 2 and the 13k resistor which might modify the resistance measured, so I feel certain of how to interpret the reading.

You still haven't answered of it moves to the correct positions with the actuator head removed from the valve body.

I thought I had. I posted on the 20th Nov: "Yes, it does". But I'm not sure that my response was indicative of anything since, as I added at the end of that same post "It's a classic intermittent problem - every time I strip it down, it starts working perfectly!"

I had a good look at that circuit diagram over the weekend and all of a sudden I realised that if both of the inputs to switch 1 are live, (and *if* the switch is working correctly!) then the switch's output should be live too (an equivalent statement to "its resistance should be zero"). So I now realise that my very first post contained the answer to my question:

I''m getting ~240V AC at both the white (CH ON) and grey (HW OFF) inputs, but (with the motor still connected) the "internal" feed to the motor (i.e the motor terminal which is *not* the blue neutral) is only showing ~63V AC.

If I'm only getting ~63V on the motor feed (the same as the switch output), micro-switch 1 *must* be (intermittently) "fubar'ed". I've just sprayed both micro-switches with contact-cleaner and it's now working. Time will tell...

Thank you, ProDave and Rob_the_rich, for your help - I think I've got this circuit understood now. With best wishes, jt.

 

[jt12345]

"so I feel certain of how to interpret the reading"

->

"so I feel uncertain of how to interpret the reading"

(I can no longer find the "edit" button) :-(

 

[jt12345]

If I'm only getting ~63V on the motor feed (the same as the switch output), micro-switch 1 *must* be (intermittently) "fubar'ed". I've just sprayed both micro-switches with contact-cleaner and it's now working. Time will tell...

Just a quick update (it's now approximately 2 months after spraying the micro-switches with contact cleaner): the V4073A has worked perfectly every day since! Result!

 

[Sharpend]

Thanks for update-appreciated