Check out some similar questions!

fslapar · Dec 6, 2008, 07:54 AM

I have replaced an older dial thermostat (one with a small vial of mercury in it) with a Honeywell RTH111/221 programmable thermostat. The heat system the old dial controlled is a boiler that feeds hot water baseboard heaters.

Since I replaced the dial with the new thermostat, the heat will not stop. The gas continues to run.

The control wire has three wires: green, red, and white.

As the RTH111/221 instructions state, I attached the green wire to the G terminal; the red wire to Rh terminal (keeping the jumper attached); and, the white wire to the W terminal.

The installation guide introduction says that a hot water system has two wires. If my boiler should only have two wires, which do I disconnect? The R, G, or W?

Thanks!

hvac1000 · Dec 6, 2008, 08:33 AM

Model number of old thermostat? I need to look up the wiring for the old thermostat. Exact brand and exact model number.

fslapar · Dec 6, 2008, 08:36 AM

Thank you.

Honeywell T87F 1859.

hvac1000 · Dec 6, 2008, 09:37 AM

OK That is the one model number. The thermostat was mounted to a item that was mounted to the wall before the thermostat. This item is called a subbase. This item is what gives the thermostat directional control. Fan off on heat off cool switches. I need the number off that item. The number might start with a Q.

fslapar · Dec 6, 2008, 09:44 AM

Hmmm. The old unit included a plate, which was attached to the wall. The portion that was mounted to that plate is where the T87F 1859 came from. This portion is also the portion that has the mercury vial attached to it.

I am not sure that I can give you the information you need...

Any other thoughts?

Thank you for your time and help!

fslapar · Dec 6, 2008, 09:46 AM

Sorry, I found it. My mistake. However, the onl number I can find on it is a "4", which is on the back. Other than that, I don't see any other numbers.

hvac1000 · Dec 6, 2008, 09:57 AM

The number for the subbase is extremely important. It is possible since you had a 3 wire thermostat that your boiler uses White Rodgers 3 wire zone valves or operator's.

Without that number I can be of no help. 3 wire boiler circuits unsually indicate a 3 wire valve. If that is the case your new thermostat may not work. The subbase part number will allow me to look up that part and see if it was for a 3 wire setup for sure.

fslapar · Dec 6, 2008, 01:11 PM

The subbase that I have does not have on-off, cool/heat, fan/auto switches. The dial that sat on the subbase is very simple - no frills. Just turn the dial to set the temperature, using the top gauge (40 to 90 degrees). The bottom gauge tells you the room temperature (40-90 degrees).

I have attached photos of the thermostat and the subbase. I hope these are helpful.

Thank you so much for your help.

fslapar · Dec 6, 2008, 01:16 PM

My system has two zones: the upper uses a White-Rodgers valve, 3/4", type 1311-102, 0.4 amps, 26V a.c.; the lower zone uses a Dayton hydronic zone valve, 3/4", 3-wire, 24V a.c. 0.4 amps.

KC13 · Dec 6, 2008, 02:46 PM

Sounds like the new t-stat is not powering the zone valve to the closed position.
The thermostat controls the zone valve, which in turn controls the boiler. If you jumper red to white, the valve opens and the internal rotary switch then powers the boiler. Jumper red to green, and the valve closes while the rotary switch breaks the circuit to the boiler. If you really want to use this t-stat, you will have to add a spdt relay to control the valve appropriately.

hvac1000 · Dec 6, 2008, 03:20 PM

Originally Posted by fslapar

The subbase that I have does not have on-off, cool/heat, fan/auto switches. The dial that sat on the subbase is very simple - no frills. Just turn the dial to set the temperature, using the top gauge (40 to 90 degrees). The bottom gauge tells you the room temperature (40-90 degrees).

I have attached photos of the thermostat and the subbase. I hope these are helpful.

Thank you so much for your help.

By posting that picture it allowed me to confirm a 3 wire configuration. Also the model numbers of the zone valves sealed that info as factual. I am not much for adding relays and complexity to anything. It would be best if you would just replace the thermostat you have now with one designed to work

Below is a list of White rodgers thermostats that will work with your zone valves. There are others available also from different companys but those you will have to look up.

1311 COMPATIBLE THERMOSTATS TABLE
Model Number Programming Options Contacts Profile Terminals
1E35-910 Non-Programmable Sealed Mercury Cell Vertical 4, 5, 6
1F35-910 Non-Programmable Sealed Mercury Cell Horizontal 4, R5, Y6
1F90-371 5+1+1, 5+2 Electronic Horizontal RC, RH, W, Y, G, MV, O, B, +, S, -, 6
1F96-344 Non-Programmable Electronic Horizontal RC, RH, W, Y, G, MV, O, B, +, S, -, 6
1F97-371 7-Day Electronic Horizontal RC, RH, W, Y, G, MV, O, B, +, S, -, 6
1F95-1277 Touch Screen 7-Day, 5+1+1, or Non-Programmable Electronic Horizontal RC, RH, C, W/E, W2, Y, Y2, G, O, B, 6, L, +, S, -
1F97-1277 Touch Screen 7-Day, 5+1+1, or Non-Programmable Electronic Horizontal RC, RH, C, W, Y, G, O, B, W/E, L, 6, +, S, -
1F97-391 7-Day Electronic Horizontal RC, RH, W, Y, G, 6, HM1, HM2, S1, S2, S3
1F80-0471 5+1+1, 5+2, or Non-Programmable Electronic Horizontal RC, RH, C, W, Y, G, O/B

1F86-0471 Non-Programmable Electronic Horizontal RC, RH, C, W, Y, O/B

fslapar · Dec 7, 2008, 06:39 PM

hvac1000 -

Thank you so much for your time and help! This list of thermostats is fantastic.

Take care...