Tankless in floor heating intermittently working..

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Evening all, I'll try to be as thorough as possible.

Issue - I have a Rinnai tankless heating solution for in-floor tiled kitchen and the garage floors, it is intermittently turning on when called for by the thermostats.

The system


It's a Rinnai v53i. The left loop is the kitchen floor and the right loop is the garage floor. There is a thermostat in the kitchen and in the garage.
Cold water line comes into Taco 329-3 pressure reducing valve
Past a Extrol model no 15 expansion tank
Then through a water pressure gauge (currently at 40psi) before entering the Rinnai v53i.

After the Rinnai there is a 75psi relief valve
Followed by a Taco 00R-MSF1-41FC multi-speed cartridge circulator
Flows down to both loops, going through a motorized valve on the left side (honeywell model no V8043F1036) and a motorized valve on the right side, i can't make out the model no of this one.
Then it's off into the floors and back through.

The electrical side of things..
The main power comes up into the emergency shut off switch - Into a 2 x 2 wall socket boxes, one with a 'winter watchmen' light thing - Into something I've no idea what it is, I assuming some kind of relay?

From that into a Taco SR 501 zone switching relay.
The power from the sr501 goes into the Taco 329-3 pressure reducing valve.

The thermostat from the kitchen goes into the left motorized valve
The out of that valve goes into the right motorized valve along with the garage thermostat which goes into the right motorized valve too.
Then the output of the right one goes into the zone switching relay and the box to the left of it.

That's the entire system - The motorized valves are working, i can feel and hear them open/close then i turn the thermostats on/off. The zone switching relay lights up red but then the circulator doesn't kick on and thus the Rinnai doesn't kick on.

When it does decide to work, once the circulator kicks on, the Rinnai follows suit and it all fires up. I'm thinking the zone switching relay is biting the bullet but maybe it's something else? What methods can i test with?



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Peace valley missouri
The zone valves see the lever below the valves wiring that is manual opener and locking it over it will stay that way till the valves motor will get powered and will close when power is taken off. With cover off the zone valves can see them stroke.Pull cover off taco sr 501 take a pic of the control so we can see the wiring.
T T terminals call for boiler when thermostat call for heat or 5&6 n.o. contact
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