Newbie needs help

Hyper35

I have a heat pump to heat my home. The heat pump has aquecoils on top of the air handler for auxiliary heat when needed. My home hot water is heated via an oil-fired boiler. The aquecoils are also fed by hot water from the boiler. If I understand correctly, I have a two-zone system. The zones are controlled by a TACO SR502-4 Relay switch. Zone one is the house hot water and zone two is the aux house heating when needed via the boiler and aquecoils. The zone one house hot water works fine. When hot water is needed the boiler starts and runs just fine and heats/circulates the hot water. The other day the outside temperature dropped into the 20's and the heat pump can't keep up at those temperatures so the system calls for aux heat, which should start the boiler to heat water for the aquecoils. The thermostat clicks and aux heat is displayed, but the boiler never starts. I replaced the TACO SR502 relay switch with a new one. Original was 20 years old, and I thought was the problem not sending signal to start boiler. The boiler still runs fine and heats the house hot water but will not start for zone two heating when the thermostat calls for aux heat. It has worked flawless for the past 9 years. Zones one and two have their own circulator pumps. Would a bad circulator pump for zone two stop the boiler from starting? Even though the thermostat clicks and calls for aux heat, could it be bad and not actually sending the signal to the zone relay switch? What else could I check before I call a pro? Hopefully this makes sense to you experts. I apologize in advance if I'm not explaining this correctly. Thanks in advacne for an suggestions.

Big Ed_4

You never mentioned using a electrical meter , I would recommend calling in a pro . Cheaper then guessing …

109A_5

Hello Hyper35,

Divide and conquer, when you expect the boiler to start because of an Aux call what is the status of the LEDs on the TACO SR502-4 (Red box on drawing) ?

" Original was 20 years old, and I thought was the problem not sending signal to start boiler. " Yet it sends the start signal from the other zone.

I would think the TACO SR502-4 zone 2 would be for the DHW with priority and zone 1 for the aquecoils. You can temporarily switch thermostat connections at the TACO SR502-4 zone connections see if anything changes (Orange box on drawing).

mattmia2

I'd try jumpering the t-stat terminals at the zone control and see if that makes it call. Are there any zone valves or just circulators? My bet would be on a bad connection to the thermostat wiring.

pecmsg

Are the heat pumps running?