Put all of your circulators on the SR503. Remove the circulator that is attached to the L8148E and transfer it to the SR503. Run thermostat wire from the X-X terminals of the SR503 to the T-T terminals of the L8148E. If you don't do it this way, you will have to power one of the X terminals with 110V and run a black 110v (hot when X-X close) back to the "B" terminal of the aquastat to fire the boiler. Use the same power supply coming from the boiler safety switch to power the SR503.

ZC/ZR terminals on the SR board go to ZC/ZR terminals on the triple aquastat with ZC/ZR terminals, using minimum 14 gauge wires. These terminals will prioritize domestic water coil. When there is a demand for heat from the thermostat, ZR becomes hot, sending 120 volts to the triple aquastat. When the boiler temperature rises above the minimum temperature setting (typically 140°), ZC becomes hot, sending 120 volts to the SR board and powering the relay for the circulators. To recap, the circulators cannot run until the boiler is keeping up with demand.

In our Control Instructions, we give two examples: a cold start boiler or a tankless coil boiler. For the cold start, the X, X goes to the TT terminals in the boiler control. For the tankless, the ZC and ZR go to the ZC, ZR terminals of the boiler. Boiler controls that don't have ZC and ZR terminals can be hooked like the cold start. These hook ups are conditional, in that you move the circulator that was originally wired to C1 and C2 over to the Taco Control.
    If you plan to leave the circulator on the boiler aquastat, and a thermostat connected to the TT terminals of the aquastat, you will need to get into the firing circuit of the aquastat. This would be the ZR connection. Run a wire from the ZR of the aquastat to the ZR of the Taco control. If there is no ZR, run a black wire from the ZR of the Taco control to the B terminal of the aquastat.
    When an aquastat has the ZC and ZR terminals, the ZC is connected to the low temperature switch of the aquastat and to the ZC terminal of the Taco control. The ZR is connected to the ZR. These will be 120 Volt wiring. When the boiler water temp is too low, the low limit switch connected to ZC opens and drops the voltage to the ZC of the Taco board, killing all the pumps until the boiler catches up. The ZR is a 120 Volt supply to the burner circuit to fire the boiler, but this goes through the high limit switch to control the boiler water temperature.

Check the heat anticipator on the thermostat for the zone or zones you think are short cycling. The thermostat should be on an inside wall, with no radiation under it, and away from outside drafts. Also check that there are no bad connections and that 20-gage wire is used, not telephone wire. The current draw should be about 1 AMP. When the boiler cycles, watch the water temperature to see if the boiler aquastat is cycling the boiler. The upstairs zone might be small and not much of a load on the boiler. You might want to lower the boiler water temperature until the outdoor temp drops. Our PC700 is an outdoor reset control used in conjunction with our -EXP controls.

Unfortunately, not with the control you have. Alternatively, you can use the SR503 as it is currently wired, but install a SR501 to energize a system pump whenever any of the three zones call for heat, and bring the aquastat from the indirect to a separate SR501 for the DHW pump, and bring the isolated end switch directly to the boiler TT terminals circumventing the system pump.

The 3 and 4 terminals are looking for a zone valve end-switch closure to close the main end-switch which is typically interfaced with the boiler thermostat terminals. If you use a two wire zonevalve without an end-switch we need to simulate an end switch closure by placing the shunt across the 3, and 4 end-switch terminals. Hopefully, this satisfies your inquiry.

The indicator light will be lit but the circulator will not come on until the boiler aquastate is above the low temperature setting and the ZC terminal puts out 120Volts

No, on like controls can be used together.

You might not get a good reading if the screw is not clamping a wire. There are test points on the board or the back of the block has exposed test points.

Yes, remove jumper on ZC &ZR of EXP board. Run a wire from P on SR502 or3 to ZC and Prioity Switch OFF

No, you need to use a PC702 and turn the boiler rotation off. The mode switch on the SR board is to be set to normal. Wire Primary pump to ZR with jumper left in the place.

On a ZVC board your T terminals at the top of the board are where your thermostat is connected. The Right Hand T is R, Left Hand T is W. Go to the bottom terminal strip, where you connect your zone valves, with terminals 1,2,3,4 and connect your C wire to terminal #1. This is your C terminal on all of the zone valve blocks.

On all of the SR multi zone boards, except the SR502 &503, the TT terminals at the top of the board are: Right Hand T is R, Left Hand T is W. You can pick up the C terminal from the Common -24 Volts terminal block next to the transformer. Note: The SR502 and 503 boards the Right Hand T is W and the Left Hand T is R

Leaving the jumper in between ZC ZR, you can put the hot leg of pump on the ZR terminal (tie neutral into neutral coming into the board). ZR (with jumper in) has a 120v output when any zone calls for heat.