Taco No Call for Heat

boulderz

Hello, I have a Lars EDP 110 boiler with 4 zone baseboard and 2 radiant zones. There is a Taco 6 zone switching relay with priority controlling the 4 baseboard zones and a second Taco 2/3 zone switching relay for the radiant zones.

None of the baseboard thermostats when turned on result in the Taco 6 zone relay to call for heat. Jumping any zone T to T does not work. All fuses look good. Wiring has not been changed and it worked in the past. The radiant zones in the 2/3 zone relay both work fine.

How can I troubleshoot this?

Zman

Do you have zone valves or circs?
Which Taco controller?

Paul48

Make sure there is 120V at the power input. If not, work back to the source. If there is 120V to the SR, check the t-stat terminals for 24V. Put one meter lead to ground and check all the terminals. If no 24V, the transformer on the SR is bad.

boulderz

null
I have zone valves. Controller is Taco SR502..

boulderz

I have 120v and 24V at the terminals.

boulderz

Just checked again and I have 24V at zones 1-3 nothing at Zone 4. All T-stats are set to low when checking. When I turn them up and check, they read no voltage, which I think is normal (checked against the working Taco SR 506)

Paul48

Sorry.....I'm fairly confused, at this point. Switching relays are used for circulator systems, not zone valves. Zone valve controls are used for zone valve systems. And. I believe in your first post, you said the 6 zone relay was not working, now you say it is.

boulderz

Sorry, I don't have zone valves. It is a circulator system.

There are 2 separate Taco switching relays. The SR506 (2 zone radiant) is working; the SR502 (4 zone baseboard) is not.

Zman

The way it is supposed to work is that the call for heat turns on the circ for that zone and closes the isolated end switch (X-X) which fires the boiler. Check the wiring from the end switch to the boiler. You could also check for continuity across the end switch.

Paul48

Someone from Taco will probably chime in. They usually watch the board, and are very helpful.

boulderz

Thank guys. On the working SR506, when a t-stat calls for heat an audible click is heard and an indicator light comes on. No such click or light on the SR502. I've swapped individual relays on the 502 with the 506 with no change.

Paul48

Coming off the transformer, you have 24v hot and common. Only the hot goes up to the t-stat terminals. When there is a call for heat, contacts in the t-stat close and pass the 24v to the other terminal, then to one side of the relay coil. The coil needs the common to function, and they probably daisy-chained the commons back to the transformer. If I had to guess, I'd say that's where your problem is. You have to be able to read the diagram on the relay and be pretty proficient with a meter to prove that out.

boulderz

As an update, as I said before I have 24V at zones 1-3 nothing at Zone 4 measured where t-stat wires connect at T T. If I remove/isolate the t-stat wire from zone 4 I can hear a relay click when other t-stats are turned up however still no activating circulator.

As a test, if I move the #4 t-stat wire to the unused 5th zone T T, again no 24v. Seems like something is wrong with that wire or T-stat. But not the whole story since still no circulator.

Any ideas?

boulderz

Another correction: none of the t-stats/zones are turning on the circulators. The only difference is the SR502 lights the LED indicators on the side when t-stats are turned on.

4Johnpipe

Do you have the jumper in ZC and ZR? These are independent controls correct? Did you jump out the TT on the top of the problem zones?

boulderz

Yes the jumper is in ZC/ZR. I have jumpered the T T terminals for all zones. Relay clicks but no circulator.

hot_rod

Sounds like you have a volt meter? is there 120V at the pump when the relay click si.
if so the pump is the problem, stuck, broken shaft or bad motor.

if no voltage at the motor check the relay that feeds the motor power going to the pump wire? if not the relay is bad or not pulling in..

boulderz

Thanks, when the relay clicks, there is not 120v going to the circulators. The SR506 has 7 24v relays plus a 120v relay. The SR502 has 2 24v relays. I tried swapping them out with a good one but no change. Not foolproof as I only checked 1 at a time but I suspect they are OK. Not burnt, no rattle. Didn't check the 120v as I don't have a spare.

There is a thermostat type wire which connects to the Laars control module. Could it be the problem or does this seem like the Taco relays?

Paul48

boulderz.........check for power to the circs, this way. Put your black lead on the "Neutral" terminal that feeds the SR, then use the red lead on the terminals of the circ in question. Let us know, if you have power that way.

boulderz

Hmm well I can't do that as the wife and I are on a 3 day hiatus. Let's hope the house doesn't freeze up!

I am fairly certain the circulators are not getting power. I did jumper from the 120v supply to a circulator and it engaged.

Jamie Hall

null

Joe Mattiello

if the green light on the control is illuminated, the transformer is good. jumping out R, & W terminals at the top of the control should pull in the boiler through XX terminals.
If the circulators are not energizing, it's possible someone pulled the factory installed jumper from ZC/ZR terminals.
If XX is not closing, I encourage you to contact Taco Tech support at 401-942-8000. thanks

boulderz

Thanks Joe, where are the R and W terminals? Don't remember those.

Edit: I have an older board so the R and W terminals are the T T terminals. Just spoke with tech support who stated jumping out T T terminals needed to be done by screwing in a wire and not touching a wire between them. I can't do that as I'm not there at the moment. Wouldn't offer any other advice until I can do this. This presumes I have 6 thermostats wired wrong or faulty...not likely. And how would it make a difference wired in or touching? When I touch a wire between them, relay clicks same as when the thermostat is turned up. No circulator.

vosac

i just went through a similarly ordeal ... The SR is run on priority mode on zone 1... untill zone 1 is satisfied none of the orther zone will start ... my configuration from the work was indirect waterheater to zone 1(priority) , air handler for home heating connected to zone 2.... when both thermostate call for heat, only zone 1 have 120v output to circ pump to water heater ... the air handler was runing cold(no heat) until zone 1 shut off .... so i change my "priority" to comfort of a heated home over hot water usage ... i put home heating on zone 1, water heater on zone 2 ... it has been 2 days since the swap ... i am still watching

boulderz

Well I had someone go to the house and work with Taco support over the phone. She had him describe the way it was wired - and couldn't believe it had worked in the past. Rewired the way she recommended and seems to be working.

The odd thing is I know I had listened to circulators running in the past (only owned the house through 2 heating seasons) but I have never touched the wiring. I'll just add this to the list of reasons why not to use the original owner's plumber (who also didn't know the Laars EBP had to be plumbed primary/secondary). Anyway thanks for everyone's help.

vosac

it is not the boiler configuration problem. it is the Taco RW S502 priority mode cause the problem ... now that it "fixed" you need to keep an eye for all of the zones if they get enough heat... you might need to increase upper litmit temperature from the boiler.