Air in House Baseboard Lines

[burnswin]

When I shift between wood boiler (Central Boiler 2400) and oil boiler, air gets into the baseboard distribution system that prevents distribution of hot water.  The system is set up as a direct connection between boilers.  The circulators push per Central's instructions.  As it is still January up here in Maine, the OWB needs to keep from freezing so the line is still open.  Is this common?  Is there something I need to do to prevent this?

The reason the OWB is down right now is the Firestar controller isn't working.  After filling the firebox in the morning I came home to a full load of wood and a dark controller.  There is power to the boiler so the controller is the problem.

[gasman1075]

Back check valves would prevent it or even manual isolation valves. You should be able to bleed the air at your oil / gas boiler in the basement of you have boiler drains on your heating loops with isolation valves. If you post pictures of the piping inside at the boiler it would help. 

[Greenerpastures]

Am from a different part of the world and do not understand your problem
other than you have air in the system.
If I had two heat sources, say a wood stove which has a boiler in it
and a gas powered boiler, I would hook up the gas powered boiler to
feed the heating system / radiators / baseboards, there will be a controller
on the gas system to cut out when the boiler temperature reaches a preset
level, that is that taken care of, though you may have zones that you can open
and close as required, and room stats that close a valve in the room when the
temperature is reached.

Now for the wood fueled set up, take a pipe from the top of the boiler in the
wood stove, and connect that to the same pipe that leaves the top of your gas
boiler, use a T joint to splice it in, put a non return valve between the gas boiler
and this T, this valve should be powered to open when the gas boiler gets the signal
to start, and it should close again when the gas powered boiler stops, I will assume
you know there should be a pressure release valve already on the gas boiler, so if
anything goes wrong the water can escape. The boiler will also have a thermostat
that will stop the boiler when it reaches a pre set temperature.


You also need a pipe from the bottom of your wood fed boiler that connects to the
return pipe from the radiators / baseboards, again just connect it to the bottom
pipe of the gas fed boiler with a T joint, no need to put a valve on it, but you can
do so to stop the water returning from the radiators / baseboards from entering
the gas fueled boiler, a manual flap valve will suffice, so no wiring needed.

To bleed the system of air, put a self bleeding valve on the pipe that feeds the
radiators / baseboards, put it on the pipe that leaves the top of the gas boiler,
on the opposite side of the T that allows the wood stove to also feed the radiators,
this one cheap small valve usually does away with air that gets in from time to time.
Its manual so no electric needed for it.

Am sure there are other connections involved that supply hot water to your for
showers, taps and such, but they are on a separate circuit than the radiators / baseboards
so should not contribute to air in the system.

Also, where I live, and anywhere else I know of, a stove that is fed by solid fuel,
coal, wood or what ever, has got to be vented, meaning there has to be a path
so the boiler in the stove can get rid of the water when its hot and a failure has
taken place such that the water is not circulating, if no expansion pipe is in place
then you will have an explosion that will kill anyone that gets in its path.
The laws where you live will outline where this expansion pipe has to be fitted,
the top pipe coming from the boiler in a stove that burns whatever you put in it
is usually where this goes, its is T 'd off and goes upward, so there is a large
enough head / weight of water present in the pipe to keep all the water from being
pushed up the pipe, the pipe usually feeds into the same tank that feeds the hearing
system, and from there overflows out a pipe and outside somewhere safe, it will be
scalding hot if its called into duty as it will be channeling water that has reached
boiling point from the stoves boiler in the event of a circulating pump failure.

Keep safe no matter what, get professional help if you can not fully
understand how your system has been installed.
REGARDING MANUAL VALVES THAT ONE OPENS AND CLOSES TO
SWITCH FROM SAY GAS TO STOVE, DO NOT GO THIS ROUTE,
IF YOU FORGET TO OPEN A VALVE AND LIGHT A STOVE YOU WILL BE
PUMPING SCALDING HOT WATER OUT THE SAFETY PIPE, THAT IS IF
THE VALVE YOU TURNED DOES NOT BLOCK THIS PIPE, IT SHOULD NEVER
DO SO.