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antique water boiler not stopping

I have an H&M water boiler which fires right up when stat calls for heat. Boiler responds to honeywell aqua stat as far as turing on and off when water temp is reached. The pump and boiler continues to run after wall stat reaches set room temp. room stat set at 62 boiler and pump still running at 64'. i lowered aqua stat to 150, boiler does respond to the different temp setting. gages (altitude) 10 to 12lb black needle, 40lb red needle hot.contacts are spotless on aqua stat and on relay which is hooked onto a transformer.
how do i get system to shut down when room stat is reached?

Re: antique water boiler not stopping

The boiler has to shut down when the wall t-stat is turned down (although the circ pump may continue running of the water temp is over 160 degrees).

The wall t-stat is a low-voltage switch (usually 2-wire red & white) that goes to a relay on the aquastat & is connected to 2 screws on the housing of the aquastat, usually inside a little metal box housing.

Remove the little metal box to access the 2 screws that contain the t-stat wires & temporarily remove them with a regular flat screwdriver---if the boiler was firing, it should stop firing as soon as the 2 wires are removed---if not, there's a short in the relay inside the aquastat & it will have to be replaced.

If the boiler DOES go off when the 2 wires are removed, short the two screws with the head of the screwdriver---the boiler/burner should immediately fire up---it should stop firing when you remove the screwdriver head---if you can get the boiler/burner to fire & stop with the screwdriver head, then there's a short somewhere in the t-stat wiring at the t-stat itself, or inside the walls.

Another issue is the red needle on the boiler gauge---the boiler water pressure increases when the water heats up---but it must not go over 30 psi on the gauge----at 30 psi the PRESSURE RELIEF VALVE at the top of the boiler should open to relieve the pressure & dump several ounces of water onto the floor---there's a little handle at the top of this valve that you can manually press to make sure the valve is opening properly---put a small pail under the drip tube---the boiler should not be run if the pressure gets above 30 psi, as this can damage the system---many of these older systems have an expansion tank between the ceiling joists that has to be drained periodically.

Re: antique water boiler not stopping

Thank you for the infomation. Upon removing the 2 wires everything shut down. Then upon jumping the 2 screws it wanted to fire up but seemed like it was straining to do so. I tested both wires fm the stat to the boiler and the resistance on both was very close, so wiring appears good. I put on a new wall stat, leveled it up and everything is running and stopping as it is suppose to. The combo gauge with a black needle on top of the red needle, is running 9lbs, while red needle appears stuck-it hasnt moved. Boiler is running at 180' The pressure relief valve is the same as the one on the water heater, 150 psi/210'.
It looks like I best find a different valve. Thankyou again.

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