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Heating, Air Conditioning, Fridge, HVAC/short cycling gas fired steam residential boiler


QUESTION: My boiler was short cycling this morning. I removed the pigtail and flushed it out. It was not clogged. I also cleared the connection back into the boiler - was not clogged. It still cycled. I drained the tank and refilled. Still cycled. Then it seemed to work fine. Does it sound like some grit or rust was lodged somewhere and was flushed out by the freshly filled tank?

Can you explain to me what the device attached to the pigtail does? Not the pressure gauge - the box with the electrical connections.
Thank you in advance for your help.

ANSWER: can you provide a picture of the device, and the boiler with piping?

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QUESTION: I will take a photo this evening when I get home but it is the pressure sensor - rectangular Honeywell bow next to the round pressure meter on the pigtail. BTW - the system worked fine all day yesterday and started cycling again this morning. Burners come on for a minute or 2 then shut off for a few seconds then come right back on. Maddening.

ANSWER: what your describing can be from a malfunctioning thermostat.  A picture of this too?

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QUESTION: I have attached a picture of my gas fired steam boiler and the thermostat as you had suggested

The Thermostat that you have there is at least 30 years old.  There is a small dial near the mercury bulbs that may be set incorrectly or has failed.  There is however the possibility that there is nothing wrong with your stat.

What I would suggest is that you TEMPORARILY take the thermostat out of the control of your boiler.  To do this you will need a small jumper wire with two alligator clips.  These are availble for sale at a tool company, Sears, or Radio Shack.  The front cover will come off of your thermostat if you grasp it from the bottom and gently move it outward, and upward.  There are two screws at the bottom of the thermostat that you can now loosen, and the thermostat will release from the back plate.  There should be a wire on the R, or RH terminal, and one on the "W" terminal.  You would use the jumper wire across these two points TEMPORARILY to determine if the short-cycling goes away.  IF any of these makes you uncomfortable you should seek out a service company to determine the cause of the short-cycling.  Reassemble the thermostat after you have performed this test.

Steam boilers require yearly service at minimum.  You should have your low water cut-off cleaned and checked.

The picture you have provided of the boiler gives me concern that the return water piping was not changed when the boiler was replaced, and is not at the correct height as required by the manufacturer.  This may also be causing operation problems.  The piping works to protect the boiler by ensuring the correct water level in the boiler so that the burner cannot overheat the cast-iron sections.  This should be checked by a company with knowledge concerning the correct piping of steam boilers.  

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Mike Reavis


Questions related to "Wet Heat". This is heating your home, office etc. with radiators, panels, and convector apparatus. Steam and water heat. I can answer questions about boilers, piping,and associated parts of these systems. Please do not ask for specific information about how I feel about one boiler, etc. over another--These questions should be directed to a licensed contractor that you know of, or that your neighbors and colleagues look to to provide solutions.


I have 20 plus years experience, which has lead to passing my state master HVAC license.


Completed college

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I work on the manufacturer's side of the business currently

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