Boiler wont heat past 120F

russor22

I have an old Hydrotherm natural draft gas boiler. I noticed one day my baseboards dont get as hot as they normally do. I checked the gauge and it will not pass 120Fish now when calling for heat. Aquastat was set at 190. I bypassed the aquastat and got the heat up to 190. So I replaced the Hydrotherms white rodgers w a compitable (according to my supply house) Honeywell 4006A. The only thing i didnt replace was the immersion well. Water still wont heat past 120F. Yes its wired in the same way it was for the past 20 years and worked fine.

mikeg2015

Pump working? A ton of mud in the boiler, so the water at the well is reaching 190, but it’s only 120 on the outlet?

Maybe the temperature gauge is wrong too. A clamp type thermocouple would be able to verify temperatures.

Lance

Check your thermostat circuit for amperage. Make sure anticipator is set right. At least. 0.6 amps. Setting varies with series circuit amps which should not exceed 1.2Amps. Make sure water pressure is at least 12PSI, or set to design for your system. Bypassing the aquastat bypassed the stat control and limit setting. Check set point again in v notch, 190F with 5 Dif and go from there. Possible bad limit control or limit.

Zman

You will need to determine if the issue is with the aquastat/sensor or the thermostat side of things. Jumping out the t-stat circuit will help determine if that is the issue. If you slowly turn the aquastat, you can usually hear a click at the temperature it is reading.
If you are handy with an electrical meter, this gets much easier.