Help with SR501 / L8124C Wiring

kentoe

Hey guys, I kept finding this site pop up in all my research over the past few weeks and was hoping to get some advice here.

This is my setup in the basement at the moment:

I have a Taco SR501 (Zone 2):

And an Aquastat L8124C (Zone 1, set to 180/160/10):


Originally, the Taco SR501 (as seen in pics) was setup in the traditional manner, but not connected to the boiler or aquastat AT ALL. So the circulation pump (Zone 2) would run totally independently of the boiler water temp, sometimes all night just pushing cold water since it's a cold water start boiler situation (no hot water off of it)

I recently referred to the SR501 wiring guide here: http://taco-hvac.com/uploads/FileLibrary/102-169.pdf

and have changed the wiring to the alternative wiring setup. I connected my wires to the ZR / ZC on the aquastat. However I have a problem: the SR501 does not work (call the circulation pump, or call for heat) unless I leave the jumper on H and 3. Could this be because there's already a circulator connected to C1?

It works exactly how I want it to right now, however my problem is that the Taco SR501 keeps 120v to the aquastat going so the aquastat thinks it's "getting a call for high heat" off of ZR. The circulation pump doesn't run constantly anymore, but the boiler keeps keeping the temperature up above 170

Any ideas?

Thanks.

HVACNUT

The alternate wiring should not be a problem. Did you splice common terminals 3 and 5 together on the 501 and bring it to ZC on the aquastat?

kentoe

Yup, yeah I have 3 and 5 together to a wirenut then a wire from that wirenut to the ZC terminal on the aquastat.

kentoe

Here's a picture of the latest wiring I have hooked up today. You can see the jumper I left in on the SR501 between H and 3. I also tried taking another wire I had and using it directly from 4 N/O -> ZR instead of the single yellow copper strand that's wired already and it didn't work.

SR501:

Aquastat ZC/ZR hookup:

STEVEusaPA

I don't like the stranded wires landing on the terminals. You're better off using solid or crimping on connectors.

kentoe

STEVEusaPA said:

I don't like the stranded wires landing on the terminals. You're better off using solid or crimping on connectors.

Thanks for your advice, are you referencing the red/black/white wire? The red wire is the only one I added. Not sure if you're suggesting that the wire should be more like the yellow.

I'm not an electrician by any means, but I am more familiar / have the red type of wire around the house. Figured this would be an easy project and wanted to get on it. Clearly it's been a rabbit hole...

Jellis

looks like if you remove the jumper between H and 3 you should be good to go with the new pictures.

kentoe

When i remove the jumper it does not work which is my main issue.

If I have the jumper in there, it works, but keeps the boiler constantly up to temperature which is not ideal.

SuperTech

It doesn't look like you have a neutral wire on the C2 terminal on the aquastat, don't know if that's related to your problem

kentoe

The C1 wire just goes to the zone 1 circulation pump which always has worked with the aquastat.

It made me wonder if the aquastat wouldn't give power to ZC/ZR if something was hooked up to C1 or C2

SuperTech

You should have a black wire from C1 to the pump and white wire to C2 from the pump as well as a ground wire. I don't know how your pump functions without a neutral wire unless you have it wired incorrectly to another neutral terminal.

lchmb

https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1351091630832/85170_PROD_FILE.pdf
Page 2..left diagram (typical wiring cold start)

kentoe

<blockquote class="Quote" rel="SuperTech">You should have a black wire from C1 to the pump and white wire to C2 from the pump as well as a ground wire. I don't know how your pump functions without a neutral wire unless you have it wired incorrectly to another neutral terminal.</blockquote>

Interesting, yeah there's only one wire going to the aquastat for that circulation pump. And the relay only has one wire going to that circulation pump.


<blockquote class="Quote" rel="lchmb">https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1351091630832/85170_PROD_FILE.pdf
Page 2..left diagram (typical wiring cold start)</blockquote>

Thanks, yeah that is how the relay was originally setup but the TT wires did not go anywhere. So no reference to boiler temp or kicking off the boiler. Should I put the TT wires to somewhere on the aquastat instead of the alternative wiring? That aquastat has it's on thermostat on TT controlling a seperate circulation pump. I just don't know why the alternative wiring isn't working without the jumper.

HVACNUT

Just to clarify, the aquastat is an L8148A right, not an L8418A like in the title? Theres no differential setting?

No wire on C2 is not a problem. The circ neutral is spliced in somewhere else.

The alternate wiring should allow cold start for both zones independently.
That's an older SR501. Its possible theres a short in the board or cube relay between terminal 3 and N.O. 4, sending power back to ZR on the aquastat therefore maintaining limit temperature.
Remove the 1-3 jumper and see if if theres 120v going through 3 and N.O. 4.

Of you need a new relay, get an SR502, wire both zones to it and use the XX dry contacts on the ST502 to close TT on the aquastat. Nice and neat too.

kentoe

HVACNUT said:

Just to clarify, the aquastat is an L8148A right, not an L8418A like in the title? Theres no differential setting?



No wire on C2 is not a problem. The circ neutral is spliced in somewhere else.



The alternate wiring should allow cold start for both zones independently.

That's an older SR501. Its possible theres a short in the board or cube relay between terminal 3 and N.O. 4, sending power back to ZR on the aquastat therefore maintaining limit temperature.

Remove the 1-3 jumper and see if if theres 120v going through 3 and N.O. 4.



Of you need a new relay, get an SR502, wire both zones to it and use the XX dry contacts on the ST502 to close TT on the aquastat. Nice and neat too.

Sorry, I may have messed up. It is a L8148A, just confirmed down here sitting at the boiler mucking around. WAIT -- **** someone put the wrong diagram on the back of the cover for a L8148A. This is actually a L8124c1003: https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1350895801607/84105_PROD_FILE.pdf

I just removed the jumped from H and 3 and tried it again still doesn't work. HOWEVER, when the thermostat calls for heat on the aquastat zone (Zone 1), the other circulator pump (Zone 2) does work with alternative wiring. It's almost as if the ZC/ZR does not kick on unless the dry contacts on the aquastat are connected in my setup. When I jump L1 to ZR, the circulator on the Taco kicks on and runs the boiler, so it's like ZR is blocked by something on the aquastat for running independently.

The maintaining of the limit temperature only happens when I have that jumper on H and 3 which makes sense.

The suggestion for SR502 is a good one, but would eliminate one of the thermostats and make it into one zone, no?

STEVEusaPA

kentoe said:

...The suggestion for SR502 is a good one, but would eliminate one of the thermostats and make it into one zone, no?

You send each pair of thermostat wires and circulator wires to their corresponding zone. No T-T on aquastat, just end switch from relay to T-T (or X-X) on aquastat.
http://www.taco-hvac.com/uploads/FileLibrary/SR502(102-082).pdf

kentoe

Finally figured out what was going on.

According to the schematic here: https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1350895801607/84105_PROD_FILE.pdf

On page 3, the only way ZR gets 120v is through B (Blue wire) for Low Limit. On my Aquastat both the blue/white wires were joined for disabling the Low Limit thus disabling the 120v for ZR and allowing the circulation pump to run.

It appears now, that the only way I can actually use a secondary zone like this on the 8124C is utilizing the Low Limit functionality. Anyone feel free to correct me if I'm misunderstanding. I connected the Blue / White wires back into the holes for low limit and it's seemingly working now like I'd expect.

If I do need to utilize the low limit functionality, $$$ wise -- would I benefit from setting my Low limit as low as possible? Like a 180 (hi) / 120 (low) / 10 diff? Or sticking with 180 / 160 / 10?

HVACNUT

No offense, but if you started with the right model aquastat, this could have been solved immediately. But this was fun anyway.
I thought the aquastat cover looked too old to match the rest of the system.
The L8124A/C is a triple acting aquastat. Its designed to maintain temp. It's not a high limit only.
Try Hi 160°. You can always raise it to 180° if needed.
Turn down the Lo as low as it goes.
Turn the diff dial to 30 or as high at it goes.
The boiler will still maintain some temperature.

SuperTech

You would benefit from switching the low limit off. Why do you have the low limit set to 160 in the first place? I don't see a tankless coil on the boiler. That seems like an awfully inefficient way to run your boiler and a tremendous waste of fuel. Turn off the low limit or better yet get an appropriate single aquastat like the L7224U.

kentoe

No offense taken, whoever installed this aquastat put the wrong model number diagram on the cover and threw me off for days. Had you not double checked me in the model number I would have said screw it. So happy it's situated. Can't believe that 😭

The low limit had always been disabled and it had been cold start from the start. Originally it was at 160 / 140 / 10 but I changed it recently to the 180 / 160 but it was never maintaining temperature.

Now it will but I set the low limit super low appreciate all the advice, keep it coming if you got it. Thank you

SuperTech

I'm glad it's all fixed, I wonder why someone put a triple aquastat on that boiler?

kentoe

No idea, just to give you some perspective -- Bought the house with it setup like this (Taco was running independently, no TT to boiler or Aquastat ZC/ZR alt wired, running off zone 2 thermostat and running all night to keep up to temp when boiler was cold and zone 1 was off) Zone 1 worked right off the aquastat.

And this was what I was referencing for a model number for the past two weeks or so: https://photos.smugmug.com/photos/i-TVGpzx5/0/e98d3444/X3/i-TVGpzx5-X3.jpg

Clearly mislabeled by someone. I checked the side mount and it had the appropriate model number.

Planning to hopefully switch to gas next winter so hoping that this boiler will be swapped out and hopefully the zoning will be setup more appropriately. If not, I'll have to look into the SR502 as a cleaner replacement.

SuperTech

That's a decent boiler and you can get several more years out of it if you have to. But I would probably switch to natural gas if it was available.

lchmb

actually you should be able to wire the control in to call the boiler on without maintaining a low limit on the boiler.. How many zones do you have total? (tstats upstairs?) in reference to going gas, the carlin gas burner works excellent in that boiler.. just make sure it's set up right..

kentoe

SuperTech said:

That's a decent boiler and you can get several more years out of it if you have to. But I would probably switch to natural gas if it was available.

That's good to know, yeah we got gas on the street. Hoping to get it into the house this year.

lchmb said:

actually you should be able to wire the control in to call the boiler on without maintaining a low limit on the boiler.. How many zones do you have total? (tstats upstairs?) in reference to going gas, the carlin gas burner works excellent in that boiler.. just make sure it's set up right..

That would be preferable without the low limit like it was before. We only have 2 thermostats (One that controls 90% of the home, the other that controls just the backroom). Right now with everything it works great with the changes I made, I just set it to 180 / 120 / 25.

Good to know about the carlin gas burner to swap out with, not that I would end up swapping that out! Definitely a professional job working with the gas.

kentoe

@lchmb what was your suggestion for eliminating the low limit new requirement from me putting both those wires back but keeping the ZR ZC still working?