Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Circulator cutting off on hydronic boiler

Duane Member Posts: 17
This weekend I attempted to help my brother with some problems he is encountering after replacing his circulator. The system is a 1930's radiator and pipoing with a 50's boiler. For the 1400sf house the radiators appear quite large to me as do the 2" headers for each loop. There are 2 headers, one for supply and one for return, on each loop, sloped up toward the convectors.

Problem 1 is the radiators will not bleed fully. The first floor sees the bottom 2/3 of the radiators hot, and the second floor they are cold. The pressure gage shows 0 when circulator is not running, and 10 psi when it is running. Opening the manual radiator bleeders gives air for a short period of time, then the air stops, whether the circulator is running or not. Hours of trying will not make the water line rise.

I believe the make-up water pressure regulator is clogged and thus is not letting in more than a slow trickle of water, if any, so the system pressure drops to zip when you try to bleed. Does this make sense? This being the case, anyone got info on how to clean out the Bell & Gossett red regulator units circa about 1955?

Problem 2 is the circulator control. When the hi limit is reached on the aquastat, the circulator turns on as one would expect and the water begins to flow. However, due to the large headers and radiators being full of cold water, the boiler temperature plummets quickly and the circulator shuts back off. I noticed the aquastat has both high and low settings, which were set at 180 / 140. The temp went below 140 in a minute or so and the circulator shut off. I know this is to preserve heat for the hot water coil, but this seems very wasteful in that the circulator starts and stops several times before serving the whole loop. What are the proper settings, considering that the large electric hot water heater uses the coil for a boost, and not for the entire job of heating domestic hot water?

Thanks and God bless.



  • Eric_32
    Eric_32 Member Posts: 267
    replace the feed

    Personally, I never had any luck cleaning out a reducing valve that old. Too much time involved draining and refilling that huge system to mess around w/ 50 year old parts. We use Watts 911s comb. backflow/ reducing valves as replacement. While ur at it, add a ball valve before and after it and make the job easier next time. no draining. The settings are generally at 180/ 160 20'dif.
This discussion has been closed.