Forced Hot Water Heating System Relay Connection

Hi, folks. I have a 3-zone forced hot water heating system in my house. One of the relays, a Honeywell R845A, recently died. I replaced it with a TACO SR501 switching relay. The new relay is working fine with the following exception: when there is a call for heat the furnace should always startup but it doesn't. The furnace doesn't automatically startup because I have not yet attached that particular wire responsible for starting the furnace. The problem is I don't know where to put that wire and I don't understand how that particular function works. The original #4 terminals on the R845A's were daisy chained and led back to the furnace relay, a Honeywell L8124A. I think that connection was responsible for turning on the furnace when the relay called for heat. When I replaced one of the R845A's with the TACO, I couldn't figure out what terminal on the TACO triggers the furnace to automatically start. I'm currently using the #4 terminal on the TACO to drive the circulator pump for that particular zone. Everything seems to work fine: when the thermostat calls for heat the circulator pump turns on but the furnace does not automatically start. The remaining unused switch terminals on the SR501 are the normally open or close switch terminals #6(N/O) or #6(N/C). The common terminal for node 6 is #5. Can someone clear things up with respect to what the L8124A needs to see in order to start the furnace. Any information would be appreciated. Thanks. Al

PS - Technical Assistance at TACO was terrible so I don't plan to contact them again. Honeywell TA was nonexistant.

The following link is for your Honeywell relay;

http://hbctechlit.honeywell.com/techlit/PDF/60-0000s/60-2481.pdf

This link is for your Taco relay which shows your terminal use when replacing the R845A;

http://www.taco-hvac.com/uploads/Product_Install/5.pdf

Hope this is of assistance.

Paul

ra relay

The Honeywell relay has the two "X" terminals for a low voltage relay/switch the Taco does not seem to have that feature and therefore, in your situation, will not operate the boiler. If it were the only relay, you could control the power to the burner through the line voltage/load switch on the relay, or the pump/relay by using the thermostat connection that turns the burner on. Since you must have two relays for yours system that option is not available to you. That Honeywell relay is very versatile because of the "X" relays and I have used it for many applications other than heating because of that feature, but you may have to replace it with another one just like it.

I already have all the technical information that ....

Hi, Paul. Thanks for the reply. I already have all the technical information that you cited in your post. I find their information, both TACO and Honeywell, lacking in so many ways. Their technical information is terrible in my opinion. Maybe it's just me and my general lack of knowledge in this area. But I do think that TACO and Honeywell could do a much better job with their technical information. For example in the Honeywell TA information they include a "Hydronic Heating Control Terminals" shown in their schematic diagram. What does ZC and ZP mean? How about a little definition of terms here on their part. Also, the same holds true for the TACO literature. What does ZR mean? Are ZR and ZP the same? And TACO makes NO attempt to describe in diagram form how multiple relays can be hooked up to control various zones in a multizone forced hot water heating system. What I need is a good general book about heating system circuits. Thanks agin Paul.

Al

hj said:

The Honeywell relay has the two "X" terminals for a low voltage relay/switch the Taco does not seem to have that feature and therefore, in your situation, will not operate the boiler. If it were the only relay, you could control the power to the burner through the line voltage/load switch on the relay, or the pump/relay by using the thermostat connection that turns the burner on. Since you must have two relays for yours system that option is not available to you. That Honeywell relay is very versatile because of the "X" relays and I have used it for many applications other than heating because of that feature, but you may have to replace it with another one just like it.

Click to expand...

Thanks for your reply. The "X" terminals that you refer to must be on the L8124A. Is that right? How did the original R845A turn the boiler on? As far as I could tell it was through one daisy chained wire from terminal #4 on the R845A. That wire originally was daisy chained between the two R845A's and then led down to the L8124A. The Honeywell schematic shows terminal #4 on the R845A connected to ZP. Do you know what ZP means? Thanks again.

Al

What you need is a double-pole, single-throw relay (DP-ST). . With the number of contacts that are on the Taco relay, you MAY have that.

One pair connects to the thermostat. Another pair act as the switch to apply power to the circulator (120vac). IF (and it appears there is) another pair, you can use that to the thermostat lead of the boiler. Basically, when the thermostat closes the relay to turn the pump on, IF the relay has a second set of contacts (a switch), it can be used to close the thermostat connection on the boiler.

I don't know where the system is getting the low-voltage to power the thermostat and relay, probably the boiler, but there could be a transformer in the Taco assembly.

It sounds like what you have here are three control relays, one on each zone, where the boiler thermostat connections are all in parallel (i.e., any one or more of them can turn the boiler on).

Assuming the Taco device does have the desired contacts, then they may be rated for different sized loads and you would want to ensure you get the right set of contacts to perform the desired task. The contacts that turn the pump on need to be able to handle more current than the thermostat pair.

Now, with this in mind, look over the spec sheets again.

This is a guess - ZP=zone pump?; ZR=zone relay?

relay

skagrock said:

Thanks for your reply. The "X" terminals that you refer to must be on the L8124A. Is that right? How did the original R845A turn the boiler on? As far as I could tell it was through one daisy chained wire from terminal #4 on the R845A. That wire originally was daisy chained between the two R845A's and then led down to the L8124A. The Honeywell schematic shows terminal #4 on the R845A connected to ZP. Do you know what ZP means? Thanks again.

Al

Click to expand...

The "X" terminals are on the diagram that your link brings up.

Possibly I am missing something but, both controllers seem to have the same number of contacts. Should just be an issue of knowing how the Honeywell was wired and do the same to the new unit.

Paul

relay

Terminals 5 & 6 are the equivalent to the "X" terminals. The burner control wiring connects to them.

Probably, but not necessarily. You need a relay with DP-ST (double pole (switch), single throw - basically two light switches controlled by one relay). If it is s SP-DT (single pole, double throw - one switch with on-off-on positions), it would have the same number of contacts, but they wouldn't work for what you want.

Basically what you need is a relay that acts as two separate single pole switches. Look at the schematics, and somewhere on it, it should say what kind of contacts are in the thing.

Okay, I looked at the spec sheet. It appears that the two leads from the other zone controllers need to go to 6 n/o and 5. n/o=normally open. n/c=normally closed. c=common. So, when the thermostat, which you have hooked to the r and w (red/white) terminals closes, it energizes the relay and connects 3 to 4 which turns your circulator on, and the same relay using different contacts, connects 5 to 6n/o which acts like a termostat to your boiler, and turns it on. The relay in the Taco is a DP-DT, double pole, double throw; i.e., two on-off type switches where each on thing is independent, and mutually exclusive. See the attached - basically, the Taco relay has a second set of contacts idential to what is shown; one set switches the circulator, the other you need to switch your boiler; each set of contacts is controlled by the separate zone thermostat which connects to the coil of the relay which causes it to energize (electro-magnet) and pull the arm which switches the connection .

The Taco install link above shows what terminals from the Honeywell get connected to what terminals on the Taco. Looks to me you guys are saying exactly what is on that spec sheet.

Looks like Al could not see the forest for the trees, have we not all been there! I sure have.

Paul