I have a 4 zone hydronic heat system utilizing Automag zone valves and one circulator. I've replaced the circulator a time or two and replaced the boiler once but the zone valves go back 35 years and work flawlessly. I can't say enough good things about Automag. Anyhow... part of my original installation was Honeywell mercury type T87F1859 thermostats which are just SPDT switches. I've been wanting to replace them with more accurate, simple (non-programable) digital ones. I've talked to the tech.people at Honeywell and other thermostat manufacturers as well as parts supply house people. No one can tell me which thermostats to use. In addition to simply referencing the current Honeywell model number and asking for a suggested replacement, I've said I want a thermostat that is a single pole, double throw switch, one that makes contact on rise and fall of temperature. You'd think I was speaking Greek... no one was able to help. Very frustrating! Anybody have any suggestions?

Why do you want single pole double throw? Rise and fall? Are you using the thermostat for air conditioning too?

The thermostat you are using would be a single pole single throw. It makes contact with low temperature and breaks contact when the set temperature has been achieved.

When you use a thermostat for both heating and airconditioning, it would be two spst switches, one set to close as temperature rises, and the other set to open as temperature rises, each set for a different temperature.

All of the electronic thermostats I have installed have hookups to run a relay for airconditioning.

Check out this link to see the various automag diagrams. They will show you how to get around your problem then you can use your choice of thermostats.

AUTOMAG - Technical Information

Gentlemen: Thanks for your quick response! Actually I talked to Jim, the owner of Automag about a year ago and he offered a direct replacement analog thermostat. Only difference between that and the current thermostats is the mechanism... probably a reed switch rather than a mercury switch. We may have also talked about a relay as shown in the diagram, I don't remember, but that's not what I'm looking for. I'm looking for a direct replacement. You may have heard the expression, "keep it simple stupid." That's my feeling on this. The less complicated the better. It would be just my luck to be out of town and the system fails because of bad relay contacts or some such thing. So in the Northeast the more fail-safe the better... I really don't want to add another component like a relay. As far as the need for a SPDT switch: the Automag system is designed so the zone valves need power to close. If there's a failure in the zone valve system all valves automatically open and all zones get heat when any theromostat calls for it... the original Automag theory being, too much heat is better than none. So in one position of the SPDT thermostat switch, the power keeps certain valves closed (the ones not calling for heat). In the other SPDT thermostat position the low voltage goes to ignite the gas boiler and initialize the circulator allowing that zone valve to open and receive heat. I have a totally separate, independent central AC system. This is unlike most modern HVAC systems which utilize a furnace or heat pump and an air- handler to supply heat or AC. So the AC system is not tied into my heating system at all.

If you have the older valves they are 24 volts DC and will not work with any digital thermostats that I am aware of since all the digital stats use 24 volts AC. That is part of the reason for the relay I believe. Sorry but I believe you are looking for something that does not exist or if found would be cost prohibitive (government use). The style relay that they are using has been proven to be dependable and I use them all the time. If you really are worried about relay failure wire two in parallel so if one looses a set of contacts or the magnetic coil the other one will be there to provide the complete circuit you need and if you are smart enough you can wire a light into the system to show any relay failure but here again that will take extra wiring so it will complicate the system .BTW I thought I would mention that my 3 zone gas boiler system is controlled by the same thermostat as the 3 central air systems. I used a split transformer thermostat and a few of those relays. The relays have been working for over 33 years without problems since the draw on the relays is almost nothing. In other words the relays see no stress or strain in every day use. Nothing more to offer here. Good luck.

NOTE: Relays are available that have open and close on each cycle to allow the zone and gas valve to operate properly

NOTE: You can also ad a Dialer to your system using a relay or extra thermostat. This way if you are out of town your house will call your cell phone number and tell you to go home because of a boiler failure or any message you so choose to place on it.I had customers who had there dialer set up to call me for service since I had a key for the homes that used that service in my key lock safe that I kept in my van. These folks never had to worry about a heat failure since we would take care of it automatically.

Since these zone valves are normally open (open with no power applied), I would think any cooling thermostat would work.

My theory is this: When set for cooling & the room gets above the stat setting, the stat would call for cooling via the Rc & Y terminals thus energizing the zone valve to close it. Once the room temp dropped below the setting, the connection between Rc & Y would be lost de-energizing the valve & allowing it to open.

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Originally Posted by Grady White

Since these zone valves are normally open (open with no power applied), I would think any cooling thermostat would work.

My theory is this: When set for cooling & the room gets above the stat setting, the stat would call for cooling via the Rc & Y terminals thus energizing the zone valve to close it. Once the room temp dropped below the setting, the connection between Rc & Y would be lost de-energizing the valve & allowing it to open.

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You're correct, upon temperature fall the zone valve solenoid is no longer energized allowing the valve to open and heat to flow into that zone. However, you still need to activate the 24 volt boiler control to light-off the burner and run the circulator, hence the need for the other throw of the single pole double throw.
PS Grady White, Delaware? I used to have a Grady White and fished out of Cape May.

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Originally Posted by hvac1000

If you have the older valves they are 24 volts DC and will not work with any digital thermostats that I am aware of since all the digital stats use 24 volts AC. That is part of the reason for the relay I believe. Sorry but I believe you are looking for something that does not exist or if found would be cost prohibitive (government use). The style relay that they are using has been proven to be dependable and I use them all the time. If you really are worried about relay failure wire two in parallel so if one looses a set of contacts or the magnetic coil the other one will be there to provide the complete circuit you need and if you are smart enough you can wire a light into the system to show any relay failure but here again that will take extra wiring so it will complicate the system .BTW I thought I would mention that my 3 zone gas boiler system is controlled by the same thermostat as the 3 central air systems. I used a split transformer thermostat and a few of those relays. The relays have been working for over 33 years without problems since the draw on the relays is almost nothing. In other words the relays see no stress or strain in every day use. Nothing more to offer here. Good luck.

NOTE: Relays are available that have open and close on each cycle to allow the zone and gas valve to operate properly

NOTE: You can also ad a Dialer to your system using a relay or extra thermostat. This way if you are out of town your house will call your cell phone number and tell you to go home because of a boiler failure or any message you so choose to place on it.I had customers who had there dialer set up to call me for service since I had a key for the homes that used that service in my key lock safe that I kept in my van. These folks never had to worry about a heat failure since we would take care of it automatically.

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You're correct, they are DC powered valves, the power supply contains a rectifier. Everything else you say is correct also. I know I can use digital thermostats if I incorporate relays. I just don't feel like going through that trouble when in fact my system works fine. I simply favor the digital thermostats like I have on my central AC system and my milivolt gas fireplace. I was just hoping to find a direct replacement thermostat requiring me to simply spend 15 minutes at each of the four thermostats with a screwdriver doing the switch-out. Again you're probably right... what I'm looking for probably doesn't exist.
By the way, years ago I used to attach a simple, single pole, single throw thermostat across the phone lines when we'd go on winter vacations and set it for about 60 degrees. While away I could call home and if the phone rang and rang I knew the house temperature was above 60 degrees. If I called and got a busy signal I knew the heat failed... which never happened fortunately. I don't think the phone company would have approved of me providing a dead short across their line if I told them of my method of checking heat from afar.

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Originally Posted by meltrol

You're correct, they are DC powered valves, the power supply contains a rectifier. Everything else you say is correct also. I know I can use digital thermostats if I incorporate relays. I just don't feel like going through that trouble when in fact my system works fine. I simply favor the digital thermostats like I have on my central AC system and my milivolt gas fireplace. I was just hoping to find a direct replacement thermostat requiring me to simply spend 15 minutes at each of the four thermostats with a screwdriver doing the switch-out. Again you're probably right.......what I'm looking for probably doesn't exist.
By the way, years ago I used to attach a simple, single pole, single throw thermostat across the phone lines when we'd go on winter vacations and set it for about 60 degrees. While away I could call home and if the phone rang and rang I knew the house temperature was above 60 degrees. If I called and got a busy signal I knew the heat failed...........which never happened fortunately. I don't think the phone company would have approved of me providing a dead short across their line if I told them of my method of checking heat from afar.

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Dang it you think like I do. LOL Yes the thermostat across the phone lines will work BUT you better get the correct wires cause the ringer of the (tip and ring circuit) will burn the heat anticipator out quickly. If I new of a stat that would work you would have a part number and wiring diagram but sorry to say it does not exist. You might already have one of these but if you do not get a indoor-outdoor (outdoor reset) control for your boiler. It will raise or lower your boiler water temperature according to the outdoor temperature. The energy savings is a guaranteed 10% to 15% no BS. Have been installing them for over 45 years and used the old analog type the went to digital about 20 years ago. Here is some info for you and it is not as difficult as it may seem.

Boiler Control 260 - One Stage Boiler & DHW

HVAC Systems

[QUOTE=hvac1000;3398479]Dang it you think like I do. LOL Yes the thermostat across the phone lines will work BUT you better get the correct wires cause the ringer of the (tip and ring circuit) will burn the heat anticipator out quickly. If I new of a stat that would work you would have a part number and wiring diagram but sorry to say it does not exist. You might already have one of these but if you do not get a indoor-outdoor (outdoor reset) control for your boiler. It will raise or lower your boiler water temperature according to the outdoor temperature. The energy savings is a guaranteed 10% to 15% no BS. Have been installing them for over 45 years and used the old analog type the went to digital about 20 years ago. Here is some info for you and it is not as difficult as it may seem.



I remember seeing that option way back when I installed my Automag system... the auto setting of boiler temp. based on outside temp. but I didn't go that route. I did install the XCS system though and it still works great. If you're not familiar with it: It doesn't do much during real cold weather when all the zones are constantly kicking in calling for heat on a regular basis. It works well on days when zones only call for heat occasionally. I have my boiler temp. set at 180 so when a zone calls for heat the zone valve opens, the boiler lights off and the circulator runs. Normally that hot water (180 degrees) in the boiler would just sit there and eventlually cool off losing much of the heat up the flu... unless another zone calls for heat. With the XCS system, when that zone is satisfied the burner shuts down and all the zone valves open and the circulator keeps going until the water temp drops to 100 degrees (aquastat on feed line). At that point the circulator shuts down and all the zone valves close and wait for the next call for heat from one of the zones. The theory is, instead of "wasting" that hot water sitting in the boiler, it's distributed to all the zones. The slight rise in temperature in all the zones caused by this extra bit of circulating hot water is hardly noticeable but it will take that much longer for any one of those zones to cool down enough to call for heat. I went a step further and added switches so I can control which specific zones get that extra heat rather than all of them. Works pretty slick!

[QUOTE=meltrol;3399166][QUOTE=hvac1000;3398479]Dang it you think like I do. LOL Yes the thermostat across the phone lines will work BUT you better get the correct wires cause the ringer of the (tip and ring circuit) will burn the heat anticipator out quickly. If I new of a stat that would work you would have a part number and wiring diagram but sorry to say it does not exist. You might already have one of these but if you do not get a indoor-outdoor (outdoor reset) control for your boiler. It will raise or lower your boiler water temperature according to the outdoor temperature. The energy savings is a guaranteed 10% to 15% no BS. Have been installing them for over 45 years and used the old analog type the went to digital about 20 years ago. Here is some info for you and it is not as difficult as it may seem.



I remember seeing that option way back when I installed my Automag system... the auto setting of boiler temp. based on outside temp. but I didn't go that route. I did install the XCS system though and it still works great. If you're not familiar with it: It doesn't do much during real cold weather when all the zones are constantly kicking in calling for heat on a regular basis. It works well on days when zones only call for heat occasionally. I have my boiler temp. set at 180 so when a zone calls for heat the zone valve opens, the boiler lights off and the circulator runs. Normally when the zone is satisfied the burner shuts down, the circulator stops and the zone valve closes and that hot water (180 degrees) in the boiler would just sit there and eventlually cool off losing much of the heat up the flu... unless another zone calls for heat. With the XCS system, when that zone is satisfied the burner shuts down and all the zone valves open and the circulator keeps going until the water temp drops to 100 degrees (aquastat on feed line). At 100 degrees the circulator shuts down and all the zone valves close and wait for the next call for heat from one of the zones. The theory is, instead of "wasting" that hot water sitting in the boiler, it's distributed to all the zones. The resulting slight rise in temperature in all the zones caused by this extra bit of circulating hot water is hardly noticeable but it will take that much longer for any one of those zones to cool down and call for heat. I went a step further and added switches so I can control which specific zones get that extra heat rather than all of them. Works pretty slick!