What happens when the radiators fill with steam

acl10

What happens when the radiators fill with steam and the vents shut? What does the boiler do does it keep producing more steam?

Joe V_2

pressure builds until presuretrol

reaches its setpoint and extinguishes the burner.  If thermostat still not satisfied, presure drops in the system and burner re-ignites. This happens until the thermostat is satisfied. 

Jamie Hall

one might add

that while the radiators are full of steam, that steam is condensing (a volume difference of 1:1800 or so!) -- which pulls in more steam.  Which condenses.  And so on.  As Joe V notes, eventually, if the boiler has the capacity (which it should) the rate at which the steam is condensing in the radiators becomes slightly less (the radiators have warmed up as much as they can) than the rate at which the boiler produces steam.  Then the pressure rises, etc.  But that can take a while -- in a really beautifully balanced system on a cold day, it may take an hour!

Rod

Be sure to consider the Vacuum!

Jamie makes a good point. You have to consider the vacuum. Venting too fast can cause a problem as it creates a huge vacuum which can result in the larger radiators "starving" the smaller ones. I have a neighbor who was going for maximum venting on his radiators and used Vari-Valves (which are very aggressive vents) on all his radiators. While these vents can be very useful in some situations they can also problems with their aggressive venting.

There is a good story on this in Gerry Gill's venting book.

- Rod