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samdobbs
samdobbs Member Posts: 8
in Strictly Steam
Hi, I am a newbie and seeking advice on replacing my Honeywell (see pic) which mostly works fine -- except a couple of times each season when it doesnt turn the boiler off even when temp is 10deg above set point.

I've seen many recs for T87, but what about any programmable T-stats that are compatible and I can diy change out my old one?

Many thanks in advance






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  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,915
    edited April 10
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    That appears to be a mercury bulb switch thermostat. They are most popular for old steam heaters like yours. Anything you purchase today will not have that mercury switch. And when you refer to the T87 thermostat, you need to be more specific. The pre 1990 T87F thermostats has the mercury bulb switch action the is popular with steam boiler professionals. The T87K and T87N thermostats are made to look the same, however they are digital thermostats with faux analogue thermometer and adjustment dial. Not the same thing, and are not as friendly with steam boiler systems.

    I believe that there are some pros that like the T6 thermostats form Honeywell (now Resideo) that have setback features that may work for you.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,014
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    Unrelated observation...

    if your Pressuretrol has a mercury switch in it, it is not properly oriented on the pigtail. Why? the mercury switch rotates in the side to side direction of the Pressuretrol. Pressure buildup (however small) in that orientation also has the pigtail rotate in the same way. Having the pigtail oriented like the pic below eliminates that possibility. Newer model Pressuretrols have a different switch. I couldn't find a pic showing what the mercury switch looks like.


  • SteamingatMohawk
    SteamingatMohawk Member Posts: 1,014
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    If you want to get creative and have additional flexibility, you could get a battery powered, wireless thermostat with internet capability. It's pricey, but you can mount it anywhere you want without wires and by getting the gateway, you can monitor the system using an app on your phone. Mine is a TH5320R1002.

  • KarlW
    KarlW Member Posts: 110
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    I had good luck with an Emerson Sensi, which is very simple but provides smartphone integration.

    (I now use a non-FCC complaint system from Europe that allows the thermostat to control the thermostatic valves - it's awesome, and I'd recommend it if it were legal).

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