Need help understanding wiring diagram - Tekmar 260 ODR with Taco SR504 Relay

Jim R.

I have a Taco SR504 relay controlling 3 pumps + DHW. Boiler has a Honeywell L8148 Aquastat. The aquastat just does the boiler shut off and doesn't operate any additional pumps or valves.

I am planning to use the Tekmar for DHW and wire it between the Taco and the Aquastat. Below is the diagram I found on google but I don't want to blindly follow it without understanding what's going on.

First, what do Taco ZR/ZC termianls do? It looks like 120v outputs but under what conditions?

According to diagram:

Taco ZR -> Tekmar 1 (Boiler Demand, input)
Taco ZC -> Tekmar 7 (Boiler Pump, output)
Tekmar 11 and 12 (Boiler output) to the Aquastat.
Tie all Tekmar neutrals together (2, 6, 8)

I assume I disconnect the Taco X/X terminals (end switch) that are going to the Aquastat now?

Can someone explain? It almost seems too easy.

Thank you!

STEVEusaPA

Well it depends a little on how the boiler is piped too. Is it primary/secondary? DHW has it's own circulator to an indirect?
Basically Taco X-X is going to go to the Tekmar to signal a demand for heating, and you may need a way to tell the Tekmar that you have a DHW call, if you want that separate.
The aquastat is just between the Tekmar and the burner, to run the burner when any demand calls, and stop it at high limit, which should be set a little higher than Tekmar's high limit.
This is assuming there isn't a pump on a boiler loop that needs to run when ever any zone or DHW calls.
And if this is for oil, or even conventional gas, you're going to need a way to protect the boiler.

What kind of boiler, and show us a picture of the piping.

Zman

This is probably more complicated than you think. If you can provide the info Steve requested we should be able to help.
This is also a good reference. https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/42742-source/260-a-06

Jim R.

DHW has it's own pump and there's an aquastat on the tank where I set the temp. They are connected to the Taco now and look like a heating zone. I planned to move those to the Tekmar as DHW Pump and Demand.

Boiler is not primary/secondary and there is no pump for the boiler alone. Each zone has a pump. Boiler is Buderus.

Pics below. Warning-- lots going on. There are actually (2) Taco's, one controlling 3 pumps and the other controlling 1 pump and 2 zone valves. They are wired similarly. I was going to understand one hookup and then see if it can be applied to Taco #2. Taco #1/#2 share the same wires going to the boiler aquastat.

I'm going with the Tekmar over Logmatic b/c... first, I was able to get a working one off a boiler being decommissioned for free, I just have to buy the sensors. Also, the idea of constant circulation isn't something the wife likes. Wants the heat ON when she adjusts thermostat up.

Zman

This is going to take some creative controls work. The trick is to figure out how to turn off the heating circulators anytime there is a call for hot water. The Tacos have DHW priority but they don't have a separate DHW switch to tell the tekmar that there is a call for hot water.

I think you have a few choices:

1. Find a different zone controller with an isolated DHW dry switch to replace the 2 you have. ( I think Caleffi makes one @hot_rod could confirm)
   
2. Go much farther down the Tekmar wormhole and let tekmar control all of it.
   
3. Learn more about controls and use DPDT relays to make this happen.
   
4. Forget about the DHW override of the outdoor reset. What model indirect do you have and what are your DHW needs? It may be able to make hot water even with outdoor reset. You will not want to use a outdoor reset with a return water temp lower than 140 anyway.
   

Jim R.

I thought DHW would be handled by moving it out of the Taco and into Tekmar. Tekmar should turn off the Boiler Pump (heating circulator output) anytime there is a call for DHW (and turn on the DHW pump).

Then my problem was-- how to control (2)Taco's from one Boiler Pump output on the Tekmar? That's where the ZC/ZR come in.

Sorry if I'm not explaining it well. I have familiarity with the concepts (not an expert by any stretch) but might be using the wrong terminology.

Thanks.

Zman

You could use 120 volt relays with the coil wired to the tekmar and the switch wired in series with the pumps power to turn them off. Not very elegant but workable...

STEVEusaPA

As far as just the domestic, what about grabbing 24v from the Taco (on the zone for DHW) and wire in series the aquastat in the indirect with the 2 contacts on the Tekmar 3 & 4. And use the 9 & 10 on the Tekmar to wire to the circulator for the indirect.
I'd have to give it a better think, but I think that would work. Then the Tekmar would reset the water temp on the DHW call.
I'm still concerned about protecting the boiler, especially on the radiant call, even though they are getting mixed downstream.
You'll probably find the ODR doesn't do much because if you put a minimum boiler temp into the control (say 140°), you'll see that you're at that temp most of the time for heating, and the boiler will short cycle.
Cast iron, zoned, probably oversized, would work best with a buffer tank.

Jim R.

For domestic... I was missing that the Tekmar needed 24v not just a closed contact. But the hookup you suggested makes perfect sense.

For sizing... boiler is 74k BTU. We're heating about 3000 sqft in Philly PA area + DHW. For the amount of water in the system to circulate and heat any zone, I don't think the boiler gets to 140 very fast. Should I be targeting a 15 minute minimum cycle time with ODR? The radiant is in concrete and doesn't call often but when it does the boiler runs for a long time (hour+) before it hits 180 and turns off.

One feature I liked on the Tekmar is post-purging. Right now the boiler is 180 degrees after a DHW or heat call, and then it cools off instead of pushing that extra heat into a zone or tank. I don't know how much energy it wastes but seems inefficient w/o a purge.

I've been on the fence about adding ODR. Figured I'd give it a try and see if it can get me any savings. But if I need to change piping or the wiring gets crazy I'll do without.

STEVEusaPA

3&4 will require some kind of power to initiate the DHW call. From the manual…

“…DHW DEMAND
A DHW demand is required in order for the 260 to provide heat to the DHW system. The 260 registers a DHW demand when a voltage between 24 and 240 V (ac) is applied across the DHW Demand terminals (3 and 4). A DHW aquastat or setpoint control is used as a switch in the DHW demand circuit. Once the 260 detects a DHW demand, the DHW Demand pointer turns on in the LCD and the control operates as described below…”

Wiring it directly to the indirect aquastat wouldn’t work.
With ODR, and other zones calling, post purge won’t do much. In all likelihood, even the the DHW target temp sets to a higher temp, the boiler may never reach that temp on a domestic call, especially if sized properly. Maybe you need to move less water on the DHW zone. But it will help a little.
It doesn’t work like the EK'S post post purge.

Life could’ve been easier with the Logamatic.

Jim R.

It seems like so much of the Logamatic control is set by a program in the unit and not very easy to make changes. For instance, if we wanted it warmer at a night we'd have to go down to the unit and override the program.

I guess Buderus doesn't make their wiring diagrams public. Would it even be included if I purchased the unit? From a wiring standpoint, what is the main difference? I understand the operation is different but conceptually it would need similar inputs/outputs. I guess my Tacos would operate in isolation, turn pumps on/off as needed and use whatever water was in the boiler but not fire it up. I think it does come with a DHW sensor so that may be it.

Trying to save some bucks for next heating season. Gas not getting any cheaper.

Jamie Hall

Wait... wait. Did you say the radiation is in the concrete? That is to say, this is radiant tubing and a radiant floor or floors, and not for instance baseboard or radiators?

From the control standpoint that's a very different ballgame. You want the radiant floors to be circulating all the time, and at a temperature set by the ODR and possibly tweaked a little by room sensors as needed. You don't say which Buderus it is, but some of them modulate, and that modulation should be what is controlled by the ODR. Otherwise the floors should be controlled by a mixing valve, in turn controlled by the ODR, while the boiler is controlled by an aquastat.

Jim R.

Boiler is G124X conventional gas.

3000 sqft, mixed emitter types. 750sqft radiant in concrete (mixed), 750 sqft panel rads w/ TRV's, and 1500 sqft fin tube baseboard. No cast iron radiators or cast baseboard. In the future the fin tube may become under floor radiant (climate panel or similar), depending on budget and renovation direction. Fin tube is beat up and in the way of some planned kitchen changes.

We did a few changes piecemeal which probably wasn't the best thing from a heating comprehensive plan standpoint, but we're happy with the performance. Wife loves the panel rads with TRV's over fin tube baseboard. One of the contractors recommended pulling out everything and microzoning but it would have been big bucks.

A lot of guesswork on what the savings would be with Tekmar / Logamatic vs doing nothing but if it's 15-30% then I'm game.

Thanks all for your advice.

Zman

Your savings for adding ODR to a conventional boiler would be more like 5%. You need a condensing boiler and all low temp emitters to get anywhere near 15-30%
I think I would consider just experimenting with a lower boiler setting. Set it to 160 and sees what happens.