Why is my new high temp zone valve addition shutting off the low temp pump?

[paul12]

For the past few years, I have used a hydronic system (outdoor wood boiler) with both high and low temp working simultaneously. The low temp system is controlled by TEKMAR mixing control #356 variable speed. I recently added 2 thermostats and 2 zone valves (Honeywell 8043F) to the high temp. All zone valves work correctly and the thermostats signal the high temp pump to turn on but also turns off the low temp pump. I bypassed the thermostat {put the red+white together}, it still kicks out the low temp system. I have 2 separate relays (Honeywell RA89A) and two separate 24V75VA transformers, one for high temp and one for low temp. The low and high temp should run simultaneously but do not. I have tried several trouble shooting tactics. There had only been one zone valve on the high temp side. That one continues to work correctly. I have tried to duplicate the wiring.
Any suggestions? Has anyone else experienced this problem? Is there a wiring diagram available for this? Thanks for your time and consideration. Paul

 

[Avo Mk8]

It sounds as if somehow the live supply for the low temperature control section is now being fed, not from a permanent live, but a switched 'call for heat' from the high temperature control section.
Is it possible that in your modifications of the hight temp. section, you have moved a live connection that was the permanent mains feed for the low temp section, to a live that goes off when the high temp section goes off.

I feel the best way of tackling this is for you to draw out the circuit diagram of what you have, which is do-able through physically inspecting it (with the power off!) and referring to the instructions of the valves and thermostats etc. A multimeter can help establish where mystery wires go if it's not obvious through physical inspection.

I would imagine the circuit schematic for your originally installed system was bespoke, hopefully documented by the installer, but It sounds like you don't have that documentation? The setup is not familiar to me (here in the UK!)

 

[paul12]

Thank you for your thoughtful response. Just to clarify, turning the new high temp on turns the low temp off. It would seem somehow the wires got crossed as you suggested. I do not have the original schematic but am able to trace most wires. I will recheck the wiring. This has been quite frustrating and I thank you for your input and welcome any other comments. Paul

 

[Avo Mk8]

Just to clarify, turning the new high temp on turns the low temp off.

I mentally had that the wrong way round then. But I think the notion could still be correct that that power for the low temperature section is, after the modifications, now coming from a component (like relay or valve wiring) in the high temperature circuit, rather than a permanent supply. If the microswitches in your motorised Honeywell valves are in use, one of those valve wires might be going to the wrong place, or wire colours confused.
Sorry I'm not being specific, I'm not familiar with the US ways of doing things!
I do understand your frustration! Best wishes for getting it sorted.

PS does power to the Tekmar mixing control unit stay on when the high temperature system turns on? (I understand it runs from a 24V transformer).
If the Tekmar is on, but not operating the mixing pump, there's probably something up with the mixing demand wiring (ie that closes the connection between pins 7 and 9 of the Tekmar

 

[paul12]

I mentally had that the wrong way round then. But I think the notion could still be correct that that power for the low temperature section is, after the modifications, now coming from a component (like relay or valve wiring) in the high temperature circuit, rather than a permanent supply. If the microswitches in your motorised Honeywell valves are in use, one of those valve wires might be going to the wrong place, or wire colours confused.
Sorry I'm not being specific, I'm not familiar with the US ways of doing things!
I do understand your frustration! Best wishes for getting it sorted.

PS does power to the Tekmar mixing control unit stay on when the high temperature system turns on? (I understand it runs from a 24V transformer).
If the Tekmar is on, but not operating the mixing pump, there's probably something up with the mixing demand wiring (ie that closes the connection between pins 7 and 9 of the Tekmar

Thank you again for your input. I have check all the thermostats independantly and find them all operating their correct zone valve. I made a wiring diagram to better explain what I have done and will attach it. I have had to order another part prior to further testing so will have to table the project for a couple of days. I super appreciate your help and will check out the Tekmar functioning when I get both high and low temps running again.

 

[paul12]

Just following up as to the cause of my problem. After spending hours retracing wires, I discovered it was not a wiring problem but in the water flow. I assumed the problem was with the wiring as that is the only thing that changed in a working system. What I discovered was the way the water flows the added demand for the high temp system was starving out the low temp. The problem can be resolved by reworking the plumbing, adding a pump or balancing high and low temp needs. I am working on the balancing plan but wanted to thank all and particularly Avo Mk8 for giving thought to my issues.

 

[Avo Mk8]

Just following up as to the cause of my problem. After spending hours retracing wires, I discovered it was not a wiring problem but in the water flow. I assumed the problem was with the wiring as that is the only thing that changed in a working system. What I discovered was the way the water flows the added demand for the high temp system was starving out the low temp. The problem can be resolved by reworking the plumbing, adding a pump or balancing high and low temp needs. I am working on the balancing plan but wanted to thank all and particularly Avo Mk8 for giving thought to my issues.

Thank you for the update. It's always nice to know that a problem has been solved, or at least understood!
Unfortunately not all those seeking advice here are gracious enough to come back and report, so thank you again for that.
Good luck with the plumbing!