Do zone valves get “tired”?

[Tim+]

Just had to replace a CH zone valve that has probably been the cause of my CH system’s intermittency. It looks like the motor is just too weak to push the valve switching mechanism far enough to trigger the micro-switch.

Oddly, this hasn’t been happening all the time but yesterday it just stopped triggering the CH altogether. Is this a normal failure mode for these motors? Just curious.

The valve itself moves freely so there’s no resistance there. The motor just seems too weak to work against the return spring.

Tim

[Davey]

I noticed when I was playing with my valve recently (that sounds like a Bishop and Actress joke!) that, operated manually, the valve opened, but the microswitch was nowhere near being operated, so the system downstream did not function. Whether this is normal, intentional, or accidental, I have no idea, but it made troubleshooting more complex than expected.

[Theo]

In my old house there used to be something similar - pump would keep running forever when the heating turned off. If I did a hard shutdown of the system the pump would stop and stay stopped when power returned. My guess is that the microswitch on the valve may have been sticky, which kept the pump energised.

(not sure why it didn't come back when power was restored, but I don't know how it was wired. 1970/80s system so not in any way sophisticated)

Theo

[The Natural Philosopher]

That can happen, yes. There is very little power in those motors and they gearboxes can dry up and add friction

Its cheap enough to just replace the head anyway.

I think I had to replace just one in 20 years.

[The Natural Philosopher]

I think I saw that behaviour on mine too. Before I replaced it.

Once replaced I no longer cared....so I dunno if its normal

[John Rumm]

If you operate the leaver on the side of the valve, then that does not usually drive it far enough to close the switch...

[John Rumm]

Th synchron motors failing is not that uncommon - sometimes "helped" by a stiff mechanism.

Usual fix is to get a new motor, take the old one off, add some oil to the valve shaft and work back and forward with pliers, until is moves freely. Then stick the new motor on.

[alan_m]

I've had problems with microswitches. The switching plunger was plastic and with a VERY small movement to get it to switch. Over the years the plastic plunger had worn down slightly and no longer reliably operated the switch.

In this case it was on a very old boiler and part of the pump over-run. It was all mechanical with a bi-metal strip operating the micro-switch plunger. When the system stopped calling for heat this parallel microswitch circuit was meant to still provide power to the pump while the boiler remained hot. When the circuit failed the micro-switch wasn't made and the pump stopped immediately when there was no call for heat. The latent heat in the burner boiled the now static water resulting in loud banging :(

[Tim+]

Indeed, I noticed that too. Not quite sure why it’s not designed to activate the microswitch in manual mode but that certainly seems to be the case.

Tim

[Fredxx]

I think practical constrains win the day. When the motor is energised it must 'unlatch' the manual mode.

If the microswitch was closed when held in manual mode, it could never move to fully open, nor unlatch the manual mode.

[Davey]

The manual mode is unlatched by unhooking the lever, which is hooked into the 'Open' position manually. It will stay there until manually unlatched, whatever the motor does. I believe, from memory. I'll check it when I get the chance.

With the manual mode not operating the microswitch, troubleshooting is made more difficult than if it did operate it. The very thing you are trying to prove or disprove is not duplicated by manual operation, which is why you are doing it in the first place!

[Peter Able]

The Honeywell specs for the valve and return spring actions are/were:

less than 12 seconds for a powered motor to complete the valve action.

less than 6 seconds for the spring to fully retract.

Check it out !

PA

[Tim+]

Well I did a PM on the old motor and it looks like it was wear in the curved rack that was the problem. When it got to a certain part of its travel the drive pinion would either jam or start slipping.

The actual drive pinion on the motor looks okay so I’ll keep the motor as a spare. It doesn’t display any lack of torque so I don’t think the motor was ever the problem.

Tim

[alan_m]

My 3 port valve doesn't. It stays latched until the motor drives it to the CH only position. Initially, and because I hadn't RTFM, this fooled me. It was summer when I filled the system and at first I couldn't work out why when I only wanted hot water the radiators would also become hot. The 3 port was latched in its mid position. Setting the controls to ch only released the latching mechanism after which the valve operated normally.

The valve is a Drayton mid position 22mm valve.

[The Natural Philosopher]

Sounds pretty reasonable. A new hear will solve that problem

The motors seldom if ever burn out. Its usually wear or corriosion or oil drying up in the mechanism.

[Harry Bloomfield Esq]

The lub dries up, the mechanism becomes less free, and they fail due to the heat, Yes. My 3-port valves, tended to last around two or three years, max. such a regular failure, I always keep one spare, ready to swap in.

[Davey]

Mine is a Honeywell. I'll try and check it out in the morning.

[Davey]

I bow to superior knowledge. It behaves exactly as described by alan_m. This also comes under the heading: "You learn something every day".

[The Natural Philosopher]

That is truly - er - shit!

[me9]

I've found mid position valves unreliable, all now changed to 2 port valves. I needed to get microswitches in bulk.