Mid position valve - springs to A port when off?

[amh15]

I'm trying to repair a Y-plan central heating system and have traced the problem to the mid position valve. It's the Tower version of this device.

The device seemed permanently in mid position and never produces a voltage on the orange wire. However, I then discovered that when it's switched off, the indicator moves to what is clearly marked as the A position (which I thought was meant to be CH). I thought it was meant to spring to the B position.

Can anyone suggest what might be going on? Has the nomenclature on these devices changed?

It looks like the screws are made of cheese so it may be tricky to just replace the actuator...

Thanks

Alan

 

[stem]

When un powered it sits at hot water only which is 'A' on the valves I have seen. This is good because most of the summer when you are don't have central heating on, it's not using any power, and the cylinder stat then turns the boiler on and off as required.

In the middle position to give hot water and central heating, the boiler is still powered externally.

In the central heating only position, the valve winds fully across, makes the microswitch that puts power on the orange lead that turns the boiler on.

 

[D_Hailsham]

I don't know the Tower valve, but could the actuator be the wrong way round?

I am confused by what is meant by

When un-powered it sits at hot water only which is 'A' on the valves I have seen.

If you mean Port A is open, then that is incorrect. But if you mean the ball (taking Honeywell as an example) is blocking port A, then that is correct.

 

[stem]

I am confused by what is meant by

When un-powered it sits at hot water only which is 'A' on the valves I have seen.

If you mean Port A is open, then that is incorrect. But if you mean the ball (taking Honeywell as an example) is blocking port A, then that is correct.

Sorry it was a bit ambiguous . What I meant was that the ball is in position 'A' closing it off and port 'B' is open

 

[amh15]

Thanks for the responses. You're forcing me to be a little clearer in my thinking.

It is quite possible that the valve is the wrong way round given the level of incompetence the installer showed (one of the radiators is installed as a dead leg with no flow through it - just a single pipe!)

However, my suspicion is that the valve is the right way round and that I am confused about the labelling. The actuator has an indicator viewable through a slot in the side of the cover. Perhaps the indicator shows which side of the valve the ball is at, i.e. which side is closed?

My current theory is therefore that the A and B markings are the opposite of what would be logical (they show where the ball is, i.e. which valve is closed), and that one of the switches inside the actuator doesn't work - the one that is supposed to trigger when the mid position is reached. Thus the grey power signal (HW OFF) never reaches the motor and the fully open CH position is never reached. I can test this fairly easily.

Thanks everyone!

 

[Agile]

Regardless of what position the valve may be in the acid test is which outlet is connected when CH only is being demanded.

I am sure all the professionals will be interested to know more about this installer. What can you tell us about him and how did you come to select him to do any work for you?

Connecting a rad as a dogleg is amusing!

Tony

 

[amh15]

Thanks for the comments. I checked with Tower and the valve labelling is indeed confusing: the indicator shows which port is blocked. So the valve is connected the right way round.

Upon investigation, I can make the valve move to the "B open" or "AB" position. I believe that microswitch S1 (the one that is supposed to switch when mid position is reached) is not switching. However both microswitches in the actuator appear to do something when operated manually (one started the boiler, the other caused the actuator motor to run). I suspect that a spring that the motor works against has corroded and thus the device is not quite reaching the right positions.

The valve is an MP3-22C. Does anyone know if the actuator can be swapped for that of their modern equivalent, the VAL322MP? Or indeed for that of the Siemens CMV322? I really don't want to drain the system down, saw off bits of pipe / olives etc..

 

[Agile]

I am sure all the professionals will be interested to know more about this installer. What can you tell us about him and how did you come to select him to do any work for you?

Tony

 

[amh15]

And for those of you that were curious, I'm afraid we have no idea who did the installation work as it was about 20 years ago when the house was converted into flats, long before my girlfriend bought the place. The other amazing trick they managed was the way they fitted the cisterns that refill the water and CH systems in the extension attic. Only a small child or a bomb disposal robot could actually reach them now, the roof is so low - I bet they fitted them before the roof was on the extension. I don't know how we would ever get them serviced now.

 

[petit_pablo]

The other amazing trick they managed was the way they fitted the cisterns that refill the water and CH systems in the extension attic. Only a small child or a bomb disposal robot could actually reach them now, the roof is so low - I bet they fitted them before the roof was on the extension. I don't know how we would ever get them serviced now.

You'd be surprised! Ive slid through a loft on my stomach to change a ball valve. There was just enough room to kneel next to tank hunched right over.

 

[Gasop]

[/quote]

You'd be surprised! Ive slid through a loft on my stomach to change a ball valve. There was just enough room to kneel next to tank hunched right over.[/quote]

You had THAT much room

 

[matt1e]

My current theory is therefore that the A and B markings are the opposite of what would be logical (they show where the ball is, i.e. which valve is closed), and that one of the switches inside the actuator doesn't work - the one that is supposed to trigger when the mid position is reached. Thus the grey power signal (HW OFF) never reaches the motor and the fully open CH position is never reached. I can test this fairly easily.

Thanks everyone!

based on

The device seemed permanently in mid position and never produces a voltage on the orange wire. However, I then discovered that when it's switched off, the indicator moves to what is clearly marked as the A position

and

Upon investigation, I can make the valve move to the "B open" or "AB" position. I believe that microswitch S1 (the one that is supposed to switch when mid position is reached) is not switching. However both microswitches in the actuator appear to do something when operated manually (one started the boiler, the other caused the actuator motor to run)

then your theory is indeed correct!!

switch 1 is getting stuck between changeover
I take it turning down the room stat or turning off CH also rests down the valve ?

if so then either the actuator at fault

or the valve is starting to "stiffen up"

either way something is causing the valve to "brake" too early when it hits the mid position or the micro switch itself has a faulty mechanism

Matt

 

[amh15]

Thanks Matt, yes, I currently believe that it's a somewhat sticky valve. It does indeed go to the rest position when room stats are turned down.

I am not going to drain the system down. I can therefore see 2 possible fixes.

1. Use whatever techniques I can to get the actuator free of the valve body, if necessary by drilling out a screw or two. Apply WD40 to the valve body and attempt to free up. Remount the actuator by whatever means available (may involve putting a bolt through where I drilled out a screw).

2. Accept that the actuator is only going to move between rest and AB positions and bodge it. The best bodge that I can envisage is a shorting link between white (pin 5) and orange (pin. Thus whenever CH is demanded and the room stat permits it, the boiler and pump will start, the valve will stick in its mid position and I will have CH and HW. Whenever CH is off or satisfied, the valve will return to HW only. The only disadvantage to this setup is that we'll have overly warm HW in the winter, but we've addressed this so far by turning down the boiler.

If anyone can tell me why one of these is a really bad idea, I'm all ears. For reference, the way it works today is room, frost and tank stats turned up to max and the valve permanently in mid position (this is the way the last guy left it). I can't see how 1 or 2 above could lead to things being worse...