120vac thermostat wire sizing

DD_5

I have a Biasi Riva boiler..wall hung..propane..non-condensing. It says that 'any external controls and connection lines must be rated 120vac'.

However the thermostat is a dry contact. I want to use the existing thermostat wire 18-24 gauge from the old boiler that I'm replacing.

Why would a dry contact need 120vac compatability? and if so, what size wire should I run from the boiler to the t-stat...?

Help...the folks at both the distributor and manufacturer are away for Black Friday.

Tim P._3

Recommend a relay

If you want to use the old wire you will need to get yourself a relay (or perhaps you have one left over from the old boiler).



That is to say, a relay rated for 120v with a 24v coil.  You send 24v to the thermostat, when the thermo closes it sends 24v to the coil on the relay.



The relay in turn closes the 120v contacts.



You cannot send 120v over low voltage thermostat wire.

DD_5

of course!

I have a TACO relay on board...its a pump relay...that'll work yes?

DD_5

of course!

I have a TACO relay on board...its a pump relay...that'll work yes?

Tim P._3

Taco relay

Yes, that should work (ie a SR501).  Instead of firing a pump use it to close the contacts to fire the boiler (terminals 5 & 6). 

DD_5

TACO 501

I put a continuity test on 5 & 6 on the TACO but it did not close the circuit. I'm wondering if the TACO doesn't function without 120vac power in. I can't add the power in because according to the BIASI RIVA manual you can't introduce voltage to the TT on the boiler. I did a voltage test on the boiler TT and read 20VAC. It seems to indicate that the TT line is actually low voltage. So the manual is wrong or there's some sort of spike that happens now and then that they want to guard against? Turns out I'll wait to talk to the distributor on Monday. Thanks for the help on this.

DD_5

TACO 501

I put a continuity test on 5 & 6 on the TACO but it did not close the circuit. I'm wondering if the TACO doesn't function without 120vac power in. I can't add the power in because according to the BIASI RIVA manual you can't introduce voltage to the TT on the boiler. I did a voltage test on the boiler TT and read 20VAC. It seems to indicate that the TT line is actually low voltage. So the manual is wrong or there's some sort of spike that happens now and then that they want to guard against? Turns out I'll wait to talk to the distributor on Monday. Thanks for the help on this.

Tim P._3

Not familiar

I am speaking about an additional relay.  I am not familiar with your boiler.



If you have an additional relay; ie something left over from your old boiler, you can use it in the manner I described.



I can't speak as to how the relay on your boiler is meant to operated (sorry, I did not realize that's what you meant when you said "on board").  Perhaps somebody else is qualified to comment on your specific boiler.