I have a 3-zone system, with 3 Honeywell Zone Valves V8043F wired in series and 3 thermostats. The problem is only 1 thermostat is causing the boiler to fire. The other 2 thermostats correctly open the valve, but do not fire the boiler.

I measured the voltage on the 3 valves with the thermostat off and on. When the good valve activates, the voltage is 24v on the thermostat wire and 0v on the endswitch (all 3 valves go 0v on the endswitch from this). The boiler is firing at this point.

When the bad valve activates, the voltage is 24v on the thermostat wire and 24v on the endswitch. The boiler does not fire. The same goes for the second valve. The bad valves do correctly open the valve. I hear the click. I even watched the microswitch get pressed down by the motor. Yet the voltage on the endswitch stays at 24v.

Does this mean the two valves are broken and should be replaced?

[table="width: 200"]
[tr]
[td]
[/td]
[td]Bad[/td]
[td]Good[/td]
[/tr]
[tr]
[td]Off[/td]
[td]0v/24v[/td]
[td]0v/24v[/td]
[/tr]
[tr]
[td]On[/td]
[td]24v/24v[/td]
[td]24v/0v[/td]
[/tr]
[/table]
(thermostat wire/endswitch)

 

Welcome to the forums.

The endswitch terminals should all be connected in parallel.

You should disconnect the endswitch wires to the valve in question. Set your meter for Rx1 or resistance if digital and connect to the end switch terminals. You should register a short when the valve is open.

 

Ok, I set the multimeter to test resistance. I turned off power to the valves.

On the good valve, when the microswitch button is not pressed, the meter shows 34. When I press the microswitch button, the meter goes to 0. Indicating a working switch.

On the two bad valves, when the button is not pressed, the meter shows 34. When I press the button, the meter stays at 34. No change at all. I hear the click, but there is no change in resistance.

Are the microswitches in those two valves broken? Is it possible to fix the switch without having to replace the $50 valve?

 

But you did NOT disconnect the wires to the endswitch when you made that measurement, is that correct? If you had disconnected them, you would be reading OPEN, INFINITE.

That's what it sounds like to me.

For a while, the endswitches were available as replacement parts, but it took a little work to change them. Most techs were not willing to do this as the time it took to change the switch outweighed the cost of a new head.

272744B - Honeywell 272744B - End Switch for Valves

You may be able to google that part number and find some still in stock someplace, if not, you will have to change the head.

Be aware that there are OLD and NEW style valve heads. The OLD style head is held to the valve with FOUR SCREWS and to change that it usually means having to drain the system, or if you're lucky and have valves to isolate the valve you can just close those valves...

The NEW style is attached with TWO screws and two 'locating pins'. You do NOT have to drain the system to change these...

The old style can be converted to the new style with a $13 kit:

40003918-006 - Honeywell 40003918-006 - 2 Way Powerhead Conversion Kit (Water)

Here is your replacement head:

40003916-048 - Honeywell 40003916-048 - Replacement Head for V8043F Zone Valves

 

Thanks! Correct, I left the wires on (power off), so that would explain the reading of 34 instead of infinite.

The valve has 2 diagonal screws inside, so it appears to be the new style.

It looks like the end switch is available on Amazon for about $20 or a new head for about $50. Not sure if it's worth fiddling with installing a new end-switch for that price difference.

I may try opening one of the bad end-switches and see if something can be cleaned to get that resistance going to 0 when the button is pressed. Otherwise, probably replace the heads and keep the old motors for replacement parts.

 

My recollection is that the endswitches are riveted in and require drilling the rivets out. The new switch then would screw and nut in, and the wires need soldered to the terminals.

For the diff in price, I would probably go for the new head. Probably take what, 2-3 hours to change that switch out the first one? Presuming that you have solder iron and know how to do that.

I suppose you could leave the wires on the terminals and wire nut the new ones together...

I've tried disassembling microswitches and cleaning them before, and it's just not worth the effort.

 

Update: Ordered two new zone valves, installed them, good as new!

I took apart one of the bad valves and tried to play with the end-switch. It was a little corroded on the plugs, but the problem was more likely on the inside of the switch itself. There was no obvious way to open the end-switch without breaking apart the plastic. So I took your advice and went with the new heads.

Note, to anyone buying a house with multi-zone baseboard heat - turn the thermostats on and test the zone valve end-switches with a multimeter. Verify the voltage is 0 when on!

 

The only sure way to measure the switch is to remove the wiring from the end switch terminals and use an ohmmeter to check continuity when the valve is the open position.

If you have multiple zone valves connected..... if one is open there will be no voltage on the end switch terminals of any of them.

 

Basically true... the usual failure mode of this type of switch is that the contacts get 'dirty' and the contact resistance begins to increase. Slowly at first... but this added resistance turns into HEAT and when the heat rises, the contacts are further damaged and the resistance goes higher... until eventually they just don't work at all.

I have measured quite a few BRAND NEW microswitches (not only zone valves...) and have found the resistance to ALREADY be 2-3 ohms. Years ago, back in the olden days, microswitches were quality products, heavy duty, would last a lifetime. Not so any more, as is the case with almost everything we consume in our disposable society.