Honeywell CH zone valve question

I did not find an exact version of the system. It is like a 'C'Plan, without the microswitch being used. A 'W' Plan uses a diverter valve, here there is only one 2-port valve, which lets hot water from the boiler circuit out to the radiators. The Tank 'stat controls the pump and boiler, DHW has to be On for heat in the system, and the timer does that. If the timer also asks for CH, then the Room 'stat opens the one valve, which then lets hot water out to the radiator loop. I am first going to check the valves etc for simple mistakes, such as closed valves, then operate the system and see what does and does not happen, hoping to do a system debug. Note that I said that the timer had been replaced, the 'new' one having a much more crowded terminal strip, so all the wiring is untested. With luck, I will be able to get it working.

Mm - I'm totally mystified as to what you *have* got.

Are you sure that your description is correct? Seems to me that, if the tank stat controls the boiler and pump, once that is satisfied the boiler and pump will stop so the radiators won't get hot even if the room stat has opened the zone valve. That surely can't be right?

A C-Plan system would have gravity HW and pumped CH and, if there were a zone valve, this would be in the HW circuit and would have microswitches. [See C-Plan in the link from my previous post] So it ain't that.

How many wires are connected to the cylinder stat? Is it just an on/off switch or a changeover. If the latter, where does the wire go which becomes live when the stat is satisfied? If boiler water continues to flow through the cylinder's internal coil after the stat is satisfied, what stops the hot water from getting too hot (assuming that the boiler flow temperature to the rads is higher than the desired HW temperature)?

Sorry for all the questions, but I'm trying to understand how it is supposed to work so that I can help with troubleshooting.

Just got back from the flat. There is heat!! The resident, Simon, is over the moon. Details later.

Ok. This is in several parts.

1. The plumber knew about the stuck pump nuts. He broke them somehow (I wasn't there) and then removed the resin'ed remains from the valves, along with the dead pump. Then he took the two new valves, and knew how to separate the nuts from the valves. Neat trick. These then went on the old valves, the new pump was installed as normal.
2. When the pump was connected, and the timer set to All on, the pump ran, and unlike the old one, has a display, showing what appears to be a discharge pressure. This was varying from 5 to 13 or so. I had checked the isolation valves, and the tank feed valve, and they were all open. The boiler would light, and then go out.
3. To cut a long story short, the whole system was one big airlock. Bleeding air from the three radiators in rotation resulted in the boiler finally staying on, and then with the zone valve opened by the room 'stat, heat began to be felt in the radiators. The pump was displaying a steady reading of 6.0 somethings. Being happy that the system was at least operating, I left for home. Soon after I arrived here, 90 minutes later, Simon called saying he now had hot water. He was ecstatic.
4. I had already had doubts about the operation of the Room 'stat before you mentioned it, but I checked my notes and that is exactly how the system was, and is again, wired. It worked for Simon all through last winter, and he had no reason to query it. In a perfect world, a better way would be found, but "if it ain't broke, don't fix it".
5. I don't see your problem with the current Tank 'stat/pump/boiler arrangement. If the tank gets to setpoint, it will shut the pump and boiler down, so I don't see runaway happening. It has never knowingly happened.
6. I had hoped to be able to use the new Honeywell 'Wiring Centre', aka J-Box, to improve and neaten the wiring to the replacement timer, as its very small terminals do not enable good tidy connections directly to it, whereas the old one had large terminals. But the new J-box has equally small terminals, offering little if any improvement. Back to the drawing board. I need to source a J-Box with larger internal connectors.
7. The Boiler/pump/valve radiator layout is as I have described it*. It does not conform to any of the published layouts. It is closest to a 'C'-Plan, but with a different valve arrangement. That is why I cannot name the Plan.

• The pump takes hot water from the boiler and sends it through the tank heater coil, and back to the boiler. Just before the entry to the boiler, there is a 'T' and the zone valve takes off from that point to go to the radiators. That's it. I didn't design it.

I need a drink.

Excellent news! So glad you got it working.

My problem with the control system is this: In order for the HW to get hot, the boiler and pump must be running. In order to have hot radiators, the boiler and pump must be running *and* the zone valve must be open. If the tank stat controls *only* the boiler and pump, and the room stat controls *only* the zone valve, what tells the boiler and pump to run for the CH once the tank stat has turned them off? Also, since the boiler and pump need to be on to get CH (but we don't know how!) in the absense of a zone valve in the HW circuit, the boiler flow will continue to flow through the tank coil even though the tank stat is satisfied. So what then stops the HW from getting up to boiler flow temperature rather than just to the lower temperature set by the tank stat? My guess is that there's something a bit cleverer going on than what you have described. Maybe it doesn't matter now that it is working again - but it would be nice to understand it completely for future reference.

I agree that the room 'stat/valve/boiler control is not theoretically optimal, which is why I was thinking about it last night. But it works. As for the runaway possibility, if the room 'stat is asking for CH heat, then there is a load on the boiler, so it is unlikely that the tank will run away as long as the room 'stat is asking for heat. When the room 'stat is satisfied, the tank 'stat will have solo control of the pump and boiler, which it already does anyway. The room 'stat does not operate them. If the tank 'stat is satisfied, the pump and boiler are turned off. I am certain that the system is as I describe it, after all, I wired it up according to my notes of it as it used to be, and I have no physical reason to doubt them. From what I see, any idea of using the valve microswitch, however conceptually desirable, would only add complications and could lead to the runaway condition you envisage. It was not connected to anything originally. One thought. We don't know how long passes between the room 'stat asking for heat and the tank 'stat asking for heat. It may be that, once the valve is opened, it takes a while for the hot water to mingle with the cold water in the radiator loop, and then the tank 'stat operates. Maybe.

You say "If the tank 'stat is satisfied, the pump and boiler are turned off." So I'm struggling to understand how, when that happens, the radiators can possibly get hot without the boiler and pump running. Can you explain that?

I can only offer:

But it works. That is all I can say on the matter. How long it takes to happen, we don't know. And I'm not going to spend £30 on petrol going there again if I don't need to just to find out. If I go again for some other reason, I might find time to experiment. If you want to fund my £30, I would consider going down again to investigate this.

I searched this morning for a suitable 'Wiring Centre', and I found this:

I fear that I may have annoyed you with my line of questioning/commenting. If so, it was entirely unintentional and I apologise sincerely. Put it down to my nerd-like desire to get to the bottom of things.

As it's now working, there's no point in making another special trip, but it would be worth having a really good look at it next time you go

-specially if you are installing a new wiring centre.

My guess is that it's designed to provide HW priority - similar to a W-Plan system - and that the radiators don't get hot until the tank stat is satisfied. If that is the case, the tank stat is probably a changeover switch with 3 connections rather than just on/off, and one of the connections probably goes to the zone valve - either directly or via the wiring centre. Hopefully you'll be able to figure it out when you're there.

It claims to be ok for S-Plan and Y-Plan systems, so it should be ok.

However, it doesn't seem to say exactly how many connectors there are. From memory, a conventional wiring centre with choc-block type connectors has 10 of them, each allowing 2 or more wires to be joined together. That's not always enough, depending on the complexity of the system. For example, mine couldn't cope with 3 heating zones and I had to install a second box.

To work out how many connectors you need, and how many wires each one has to accommodate, you really need an accurate wiring diagram and I'm not sure that you have one.

Apology accepted. I understand not understanding something technical.

I can assure you that the tank 'stat has only 2 wires, Live and Load. The Room 'stat has 3.

At the moment there is no wiring centre, but hopefully there will be in the future. I will engage a professional electrician to install it, if I can find one. At the moment, the plan would be to exactly replicate the current unsightly and crammed-in wiring, but with the Wiring Centre included, making the whole thing sensible and easy to work on.

Everything appears to work, except why does the Room 'stat not need to run the pump and boiler? I have proposed a theory. The next time I am there, that is what I will investigate, time permitting.

Reverting to the original problem, the burnout of the timer, I am thinking that it might have occurred when the pump failed. It might have caused a sudden jump in current passing through the circuit as the pump stalled, or failed to start. Just conjecture. When I went there the first time, and discovered that the pump was dead, although it had power, the end of the shaft, visible under a removable cover on those old pumps, was not moving. Still, it had been running since 1976, so I think it did its job. The Danfoss pumps seem to deserve the term 'bullet-proof'.

In the farnell "documents" section they show how you'd use the wagos in a "Y" configuration, but it doesn't show an "S" version ...

I have downloaded the 'Y' diagram, and have already marked up some of the changes needed. These include changing Terminal 8 to a 2nd Earth block, as the Room 'stat has one as well, and so does the timer, and terminal 8 is not needed for the non-existent 2nd wire from the Tank 'stat. Some wire colours are different, too. There is no hurry.

With the zone valve where you said it was, I am wondering whether the water flow through the pump is in the direction you assume it is. If you imagine the flow through the pump is in the opposite direction you have (as near as dammit) a C-plan system.

I wondered about that but dismissed it because Davey's system appears to be fully pumped - whereas C-Plan has gravity DHW - and C-Plan has the zone valve in the HW - not CH - circuit *and* uses the valve's microswitch.

Snipped.

I am certain that the flow is as I described. I had to re-orientate the pump body before installing it, as it is horizontal flow instead of the default vertical flow, and it was checked by the plumber when he managed to sort out the valve securing nuts and install the pump. The flow arrow can be seen now it is in place, it definitely matches the original pump, and the pump body clearly defines its operational direction. As far as I can see, the system is working, Simon is warm, and the only thing left to do is to fix the wiring with a 'Wiring Centre', probably the Wago one I found, it fits the bill. The only mystery is how the pump and boiler are energised when the Room 'stat calls for heat, and I will check that when I am next there. Whenever that is.

I think I have solved the mystery. The timer does not offer DHW-off/CH-on Operation. So if the room 'stat is enabled, the hot water is already running. Simple! Since I am thinking about replacing the ancient Randall with a modern digital timer, I need to make sure that it has the same arrangement internally. Another day.

Big snip for brevity.

I followed the trail online which leads to the recommended replacement for the existing analogue timer. Looking at the Danfoss information online, it provides tons of information about how versatile the programming is, but nothing to indicate if the same setup regarding the DHW power is available. I e-mailed them, and ..........nothing yet. So I have a question for the electronics folks here. I have modified the wiring diagram to use a digital timer that separately powers the pump and boiler when the valve microswitch is activated by the Room 'stat. My question is: Is there likely to be any harm done to the electronics in the digital timer by feeding power from the microswitch to the terminal which is the DHW control in the timer, ie backfeeding it from a different location? It is still the same power, but feeding the load side of the DHW terminal. I am concerned in case the electronic component that usually makes the connection might not like power being applied to its load terminal but not its internal supply terminal. Maybe it is not even a consideration, but maybe it is. i will also ask Danfoss, once I have established communication with them, but if anyone has any input, it would be most welcome.