I just finished installing a new radiant system, coupled with an old boiler that needs protection from return temp below 140F. I installed a 4-way mixing valve (ESBE) and a teckmar 360 mixing control.

In the manual of the Teckmar 360 it says that if its the only control unit then the boiler sensor should be placed on the supply side of the boiler, However, my main concern is that I want to make sure that the return water is never below 140F so it makes no sense to install the sensor on the supply side. There is an option to install it on the return side, but the control of the boiler uses a "boiler enable" function, and it is only recommended if this one of multiple controls of the boiler.

To test the mixing valve and the teckmar 360 I tried the two configurations:

1. I installed the boiler sensor on the return side. It successfully adjust the mixing valve so the return temperature is always above 140F, while trying to meet the system design temperature. The problem is that it leaves the boiler always on. Even when the mixing valve is completely closed it still calls for heat. The boiler has a temperature protection setting that shuts it off, but it leaves the boiler pump always on.

2. I tried installing it on the supply side, and in this case it correctly adjust the system temperature that goes to the radiators, and turns off the boiler when enough heat is in the system. However, it does NOT protect the boiler, as the return temperature goes far below the 140F limit set in the teckmar 360.

Any ideas on how to setup the system so that it BOTH protects the boiler AND shuts it down after the heat demand is met?

The only way I can think how to make it work is to pair the teckmar 360 with the teckmar 256 (boiler control). The 360 deals with the mixing valve to protect the boiler from low return temperature and to meet the mixing temperature of the system. The 256 reads the 'on/off' boiler enable from the 360, and reads the supply temp of the boiler. With these two variables it turns the boiler on and off.

But there has to be a simpler and less expensive way to do this.... Ideas? Thank you!

 

How have you got the system piped?

Which diagram in the 360 application brochure are we looking at?

 

I have it piped in a very similar design as the attached image. The only difference is that I've added a valve to the boiler loop so I have the option of manually controlling the flow in that part of the system. Given that there are two pumps in the system I wanted to avoid the potential, when the mixing valve is at 100%, of both pumps in series.
BTW the image is from the teckmar essays E021.

 

Won't happen... as long as you've got the closely spaced tees on the boiler loop, there is 'hydraulic separation' between the two pumps. One pump won't affect the other in that situation.

You DO have the piping on close spaced tees on the boiler loop, correct?

 

Yes I do have the piping, I've just added a manual valve to the loop. Currently it is wide open.

Regarding the original question. Do you have any idea of how I can modify the system so that I can both consistently protect the boiler from flue condensation (min 140F return) and have the teckmar power off the boiler when the system heat balanced is reached?

Thank you.

 

Can you show us some pictures of the piping loop around the boiler, and to the 4-way?

Before troubleshooting a control problem, I want to SEE that the piping is correct.

To what do you have the boiler loop pump wired?

 

By what means are you measuring the return temperature to the boiler?

And the 'limit' you speak of, do you mean "BOIL MIN" ?

 

I am curious about your return temp target. Is this boiler gas or oil fired?

Pete

 

Seems like he gave up on us... last login was time he posted last message... oh well.