Honeywell CH zone valve question

The lever typically does not move when the valve is energised.

However, if you manually move the lever when the valve is energised you should encounter much less resistance as you move it, and it should stay put in the "open" position without being hooked in place — only returning to the "closed" position when power to the valve is removed.

Stephen Early

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Thanks, that is important information, that the ever does not move when the valve is energised. So it might still be good. Hmm. More thinking to be done.

Cheers,

There is a microswitch inside which closes when the valve is fully open and tells the boiler to switch on - does that operate under both manual and energised conditions?

You can generally hear the motor running when its energised. For s second or so, before it stalls. At that point the valve is open and the l.ever goes 'floppy'

Now if the valve is seized the motor will stall immediately with the valve closed. And the lever wont go floppy.

The next step is to remove the motor unit off the valve and run it away from the valve,and also try and turn the valve stem with a pair of pliers. I have successfully repaired valve units both by freeing up the valve turning it by hand to break up scale and also by replacing a dead motor unit.

The fact that the lever moves easily, and returns, implies that the valve itself is not seized. In this system, the microswitch is not used.

As I mention in another Reply, the microswitch is not used in this odd system. I have had the situation on a different system where the switch was made with the valve energised, but not when operated manually. Very helpful.

Can be seized open, but normally yes.

Yes.

If there is a call for heat on the zone, the valve and motor should move.

If it fails to move, when there is a call for heat to the zone, then likely the motor had failed. You can buy just the replacement motor, or a complete replacement actuator head.

If you don't latch it, it should be returned to the closed position, by the spring. The latched open position is used when filling the system, to prevent airlocks. Once powered open, the latch should release.

In this case, the replacement head needs a kit to update it, apparently the old style valve did not allow the head to be removed without all the valve internals coming apart, so needing a drained-down system. The kit is a one-time conversion, that the allows the headend alone to be repaired.

As far as I can see at the moment, and this is not conclusive, it looks as though the valve moves freely, but the motor may well be dead. The manual operator does exactly what it is supposed to. Remember that I have only investigated this once, a few days ago, and I will be there again on Boxing Day. I will change the dead pump first, and see how that goes. Draining down and refilling the system would (will?) take an age, the water supply is not fast, and I don't know at the moment how I could drain it. That would be for another day. This whole system was installed in the flat in 1976, so it has lasted remarkedly well. Even the boiler is original.

This one 'has legs', as the saying goes.

Update. I went down to the flat on Boxing Day to change out the pump Application of heat, and attempting GBH with a hammer, did not work, and the two of us could not separate the first of the two securing nuts that hold the Danfoss pump in place in the pipework. The whole pump rotates taking the nut with it, it rotates about its flange. We had to admit defeat, and regroup. Of course, finding a plumber at this time of year is well-nigh impossible. We took a good look at how to drain the system if necessary, and there is no provision whatsoever, not even a drain point. And the only way to get rid of the water (or whatever comes out) is via a hose trailed downstairs and out the front door. As far as we know, the system is exactly as it was installed in 1976!

Next thoughts are to look at removing and replacing what holds the nut's flange. But this risks needing to drain the system. The nut's flange seems to be attached directly to the isolation valve, even a part of it, on both sides, so replacing the flanges on the valves would certainly need the whole system to be drained. Was/is a valve with the Danfoss pump nut incorporated an actual item? I find the Danfoss website impenetrable.

At least the electric heater works, but costs a bomb to run.

The isolatiion valve is separate from the pump and not part of it. The pump ends with a flange with a male thread on the outside, like this.

Provided that (a) the isolation valves work and (b) that you can separate them from the pump by the method described above, you can change the pump without draining down.

Easy to say...

If we could separate them...

That is what we have not been able to do. The threads will not separate. But thanks for confirming the arrangement of the valve and flange, it is exactly what we have.

OK, even if you can't separate the pump from the valves, you may still be able to change the pump without draining down.

You'll need to turn off both valves on all radiators to stop them emptying and, assuming it's an open vented system, you'll need to bung up the outlet from the fill & expansion tank and bung up the open end of the inverted J shaped exansion pipe. You can then break the system in

You need to go armed with the new pump and two new isolation valves. Turn off both existing and both new valves. You can then undo the compression nut on one of the old valves and, assuming there's enough movement in the pipes, separate it from the pipe and immediately fit one of the new valves in its place - using the original olive and compression nut. Then do the same with the other one, and remove the pump complete with its two valves. Immediately fit the other new valve.

You'll then have two isolation valves at the right spacing to slide the new pump - along with two rubber washers - into position and do up the ring-nuts.

Then, turn the radiators on again, unbung the bunged up bits, turn on the isolation valves - and the job's a good'un!

Don't suppose you have any photos of the existing pump installation which you could post somewhere with a link here? That you give us a better idea as to how much of the above is feasilble.

If the system is *really* old, you may have imperial sized pipes rather than metric - which could present some additional challenges!

Snipped for brevity.

Reply No 1, No 2 to follow later.

The last item has been worrying me. The system was built in 1976, when the house was converted to flats, and that had me thinking about the piping used. Does 22mm copper pipe correspond to a 1976 Imperial pipe size? I have been looking at various charts, and have only got very confused.

I have an old photo, and I have asked for a newer one to be made available, but that has not happened yet.

I had a Dropbox account, but it has lapsed. What is a good alternative place to put photos for general viewing?

If the pipe is imperial it will be 3/4" nominal - which is actally larger than 3/4" in reality, and *slightly* smaller than 22mm. If connecting one to the other with soldered joints you need special fittings with 3/4" one end and 22mm the other end. With compression joints there's a bit more leeway. A 22mm fitting is ok on a 3/4" pipe (but not the other way round) but you need special olives with a slightly smaller ID. You'd probably get away with replacing an imperial pump valve with a metric one because the 3/4" olive already on the pipe should be ok, and the compression nut threads will almost certainly be the same.

For posting photos I always use Box - which is similar to Dropbox - but there are other free options. Hopefully someone who knows more about it than I do will come along . . .

That is good news! I know that when I started employment, in late 1972, at an engineering company, one of the old-school engineers was talking about the ongoing metrifucktion of engineering standards.

I have just checked the part no. of the Zone valve, and it comes up as a 22mm valve. So that is a good sign. Hopefully I can order two new isolating valves to take with me when I next go to the flat, armed with some more powerful pump-removal tools.

I'll look into Box, thanks.

Update. The resident in the flat managed to get a plumber yesterday, and he succeeded in changing out the pump. The reason that we could not was because the nuts that hold the pump and the isolating valves had been cemented or glued in place, and so the valves had to be replaced at the same time. Now the pump runs, but the storage tank does not get hot. The resident is not electrically-trained in any way at all, so has no way of checking what is or is not happening. He suspects the tank 'stat wiring. I hope to find out tomorrow. He will try today to engage an electrician for next week, I plan on going there tomorrow if no electrician is forthcoming. But there is progress! Now I have a spare set of valves, and a very wide mouth adjustable spanner purchased to better attack the pump securing nuts. But you can never have too many tools.

I had wondered if there might be an airlock, but the fill and expansion tank is directly above the cupboard that contains the boiler, pump and the storage tank etc, so I don't see how there could be an airlock that does not instantly bleed out.

On 03/01/2026 10:19, Davey wrote: <snip>

The fill and expansion tank is for the water supply for the boiler and radiators. There should be another source of water for the tank contents that goes to the hot water taps. Have you checked that the second source is sufficiently full? If it isn't the hot taps should stop running, so that is probably the easiest to check.

Perhaps the zone valve isn't opening to heat the water? Try opening it manually and leave it hooked open and see if there is hot water after running the boiler a bit? Also, check the programmer settings. On my system the Hot Water ON/OFF circuit controls the zone valve on the hot water circuit and the Heating one controls the circulating pump for heated water to the radiators, so that I can have one or other or both in operation. I have never tried the hot radiators and no hot water option, but that is the scenario controlled by the frost thermostat to stop the system freezing if I am away for any length of time in the winter. Either controller being on will allow the gas through to heat the boiler.

As an aside, I did use the microswitch circuit in the zone valve, it lights a neon when the hot water control is ON and the tank thermostat interrupts the zone valve circuit when there is sufficient hot water in the tank. In a nutshell, if the neon is off then either the hot water ON/OFF is off or there is insufficient hot water which causes the thermostat fitted half way up the tank to demand heat. The default of the neon being on is to show that there is over half a tankful of hot water available and it will reheat if I use enough hot water to have more than the bottom half of the tank refilled with cold. It gives me an at-a-glance reassurance that the hot taps will deliver hot water.

Thanks for thoughts. I am going down there tomorrow for sure. I had already made a list of things to check, such as: Valves open, including header tanks' supply, pump pointing in the right direction, is the pump really powered, water available at taps, etc etc. I realised that the boiler and pump would not run unless the tank 'stat was asking them to. The zone valve only controls the radiator branch, determined by the room 'stat, the boiler and pump both run according to the tank 'stat. If the tank 'stat wants heat, and the timer is 'On', then the pump and boiler should run until the tank is hot enough. The radiator loop comes afterwards.....and heat lost there will drop the tank temperature, and so on. The whole thing that started this was the burning out of the old timer. It had a very good set of wire terminals, so the lack of a Honeywell J-Box was no problem. The replacement has a much smaller terminal strip, so I have bought a Honeywell J-Box for future installation. But at the moment, the timer is hanging from the shelve above by a wire, and although I believe the wiring is correct, tomorrow will be the first time I can check it out empirically. Wish me luck!