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How to troubleshoot a Taco Zone Valve
This is the Taco zone valve. The head on yours may be
blue green instead of gold or brown. The top (#1) terminal
is the power to the zone valve The middle (#2) terminal is
the common terminal. The button (#3) terminal is the end
switch. 24 volts to 1 and 2 opens the zone valve.
If the thermostat is turned all the way up and you do not
have heat in that zone. test to see if you have 24 volts AC
at terminals 1 and 2.
Click on any image to see a larger image.
If you do not have power to 1 and 2 the problem you are
having is not with the zone valve, but before you move on
make sure that you have turned your thermostat all the way
up, This means as high as it possibly goes. then if there is
no power at the zone valve the problem is not with the zone
If you do have 24 volts at terminals 1 and 2 and have waited
at least 2 minutes, check the lever.
Pull down on the lever, if the lever goes all the way down with
no resistance, the problem you are having is not with the zone
valve. If there is resistance, and you have 24 volts at terminals 1
and 2 and you have waited at least 2 minutes, the power head and or
the whole zone valve is defective and needs to be replaced,
Danger Removing a hot power head can be dangerous.
Make sure The power to the zone valve is off, and has been off for
at lease 2 minutes. Just turning the power switch off does not mean
the power to the zone valve is off. Remove the top (#1) wire if you
are not sure. Make sure you wait 2 minutes before you proceed. If
there is enough slack in the wires, grab the head and turn it 1/8th
of a turn clockwise, and lift, put the new head in by doing the
reverse, Then move the wires to the new head. If the new head burns
out soon after you have replaced it, you will need to replace the
whole zone valve.
In this image I am getting a hold on the Taco zone valve power head, getting ready to turn it.
In this image I am turning the Taco zone valve power head clockwise 1/8th of a turn.
In this image I lifted the Taco zone valve power head from the Taco zone valve body.
This is what the bottom of the Taco zone valve power head looks
like notice the two black pins, they go into the slots on the Taco
zone valve body, just line them up and turn 1/8th a turn and the
head is replaced.
This is the Taco zone valve body, sometimes this part of the
zone valve fails, The 2 problems I have run in to are, one the part
of the zone valve that is pushed by the head gets stuck and will not
move freely, this will cause the power head to pop or burn out. Two
the part that the power head moves, does not go all the way back up
when the zone valve is no longer calling for heat, causing you to
have heat when you do not want it, in both cases the whole zone
valve needs to be replaced.
Why do I keep saying wait 2 minutes? A Taco zone valve is designed to open very slowly, by heating wax that expands and pushes a plunger
that opens the zone valve. It takes about 2 minutes for the wax to fully expand.
and the same to contract, removing the head while the wax is hot and under pressure can cause the plunger to pop off, the flying
plunger can hurt you, and the hot wax can cause a serous burn.
So what is the problem, if I do not have power to terminals 1 and 2? If you do not have power to 1 and 2 either the transformer is
bad or your thermostat is bad.
So what is the problem, If the lever does go down with no resistance and you have 24 volts at terminals 1 and 2?
1- your boiler is not running, 2- Your circulator is not running. 3- your zone is air bound 4- your zone is frozen
5- you have a broken pipe under a slab. There are other reasons. For further help with this type of problem,
Please use the Open Dialog Service.