steam one pipe radiator issue

Matt_S

Good afternoon all,

I have been having issues with an office since the begining of heating season.  Her radiator keeps getting too warm, even when the thermostatic valve was turned all the way down.  I figured this is a pretty easy fix and decided to change out the thermostat on the valve since it wasnt regulating.  Later that same day she called and said it was still too warm even though the thermostat was turned off.  It was late in the day and supposed to be 60 the next day so I shut off the hand valve to the radiator and fix it another day.

Fast forward to today and she was cold.  I recalled the issues last time and decided to change out the entire valve, thermostat and air vent.  I verified operation of the thermostat and valve beforehand by watching it open and close while turning the knob.  I assembled everything, turned it on and the air purged from the radiator.  I spoke with her and decided to turn it down a little. The purging stopped, so I assumed that the heat would stop.  A few hours go by and she turned the thermostat all the way off and the radiator was still blazing hot nearly 3 hours after shutting off.  If the valve is seated all the way, how is this steam getting in to heat the radiator?  The only thing I can come up with is a steam leak on the cast iron somewhere and it is seeping out, but I do not see any wet spots on the carpet.  I am going to check into it again tomorrow for a little, but plan to work on it on Thursday. 

Any suggestions on what may be going on? Or any additional information needed?

Hap_Hazzard

The heating doesn't stop when the air stops venting.

You might say it's just getting started. Radiators work by turning steam into water. How much water? One cubic foot of steam condenses down to just a little over a cubic inch of water. That's about six hundredths of a percent. That leaves room for a lot more steam, which also condenses, allowing more steam to… well, you get the picture.



A standard radiator vent will close when the radiator fills with steam and remain closed until the the thermostat stops the boiler, the system begins to cool, and the pressure falls below its drop-off point.



A thermostatic radiator vent senses how warm the room is already, at the beginning of each cycle, determines how much heating is required to make up the difference, and allows just enough air to escape to allow just enough steam to enter, to bring the room up to its target temperature by the end of the cycle.



The steam will still collapse and allow more steam to enter, but if the radiator is, say, half full of air and half steam, the radiator will only be condensing at half its maximum rate. (Actually a little more, because the surface are doesn't change, but I'm trying to simplify it.)



So the trick to making it work is finding the right set-point to let in just the right amount of steam before shutting down the vent. This can take a lot of patience and persistence. To keep from losing your mind, make sure you record the setting each time you adjust it, because people will fiddle with it. If you don't keep track of the adjustments you have made yourself, you won't know what the hell is going on.



But just remember, the radiator will continue to heat throughout the cycle, even after the vent closes. The trick is to make the vent close when just enough steam has entered that it will reach just the right temperature by the end of the cycle.

ch352

Perhaps

Missing Vacuum Breaker?