Ron – We are back. If you missed the last three shows, we have Joe Contractor with us and we are discussing multiple high efficiency boiler installation and set-up. Joe had many good questions and we invited him back for a fourth and final time. Joe, in the past few shows we talked about mix and matching boilers, piping, and venting. You wanted to come back this month and ask some questions about the control set-up for multiple boilers.
Joe – Yes, I feel like I understand so much more about installing multiple high efficiency boilers! But, I do have a lot of control questions. I believe this is probably the hardest part to get right on these installs.
Ron – Actually, Joe, the control set-up is very easy.
Joe – Really? I hate to admit it, but I do struggle sometime with these newer electronic controls.
Ron – I guess the first thing to remember is when doing multiple boilers, you are required to have a header sensor installed. If you do not, you will not be able to enable a master boiler. I would also like to remind our readers that a header sensor reacts much faster to temperature changes if in a well in the system piping than a strap on sensor. We should also have a Cat5 cable connected between all the boilers utilizing the boiler to boiler connections and the intermediate boilers using cable splitters.
Joe – What if I cannot find the splitters? I looked locally and find them hard to find.
Ron – When you are preparing for a multiple boiler job, you can order splitters from us using part #103192-01. What if you are on the job and do not have splitters? Alternately, the network can be wired together by simply wiring terminal J3, Modbus 2, terminals A, B and V-between each boiler.
Joe – Wow! That is good information in case of an emergency. Okay, lets talk programming. How do we enable the master? Do I have to turn on the header sensor somewhere?
Ron – I will answer your last question first. We do not have to enable a header sensor. When we enable the master boiler, it will determine if there is a header sensor connected. If so, the control will allow you to enable the master. After you complete the installation and are ready to set-up the control, you must first log into the control. The parameter menus are found in the “Operation Section” of the Installation & Operation manual. When you first log-in, you will see the System Set-up menu. In the slave boilers only, find the OD sensor and select “Not Wired.” This will disable the control from looking for an OD sensor on the slaves as the master boiler is the only one that you would connect an OD sensor to. Find the Sequence Master menu. The first screen will be the Enable/Disable parameter. Enable the master boiler.
Joe – That sounds easy enough. Is that all there is to it?
Ron – No, not quite. Before we go to the second necessary control set-up step, I will touch on other parameters in the Sequence Master menu that you may want to address. Here is the list of parameters under the Sequence Master menu:
- Indirect Water Heater – If there is an IWH connected to a multiple boiler installation, you would wan to address it here.
- DHW Two Boiler Start – I normally would leave this in one boiler start unless the IWH is large enough to require both boilers. The control will start more boilers as needed.
- Boiler Start Delay – Default 180 Sec.
- Stop All Boilers – All boilers are stopped without delay if the Call for Heat input is removed, or, if the header temperature is higher than 195°F. Do not go higher, but in some instances, you may turn it down.
- Base Load Common rate – Default is 70%.
- Response Speed – Unlike the response speed setting under central heat which applies to just one boiler, this setting applies to all boilers in a multiple boiler application.
We will use the “X” (back button) in the upper right-hand corner of the screen to return to the menu choices. This time select the Sequencer Slave menu. There are two options here. Boiler Address and Slave Selection Order. Every boiler requires a boiler number between 1 & 8, including the master boiler. It does not matter which boiler gets what number as long as they all have a number. The master boiler does not have to be number one.
After this programing is done, we turn the power to each boiler off and energize the Master boiler first. When the screen initializes, turn on all the slave boilers. You are done.
Joe – Hey that sounds extremely simple, short and sweet! Just clean-up and get out of there!
Ron – Whoa, I did not say we were done. You can make the boiler more efficient by fine tuning the ODR curve and zone panel through the display. After that, there one more important step.
Joe – Oh yeah? What’s that?
Ron – The start-up. Here is my official list and notes for start-up:
- Gas pressure check – Verify the gas pressure is within the specifications for the boiler rating plate. On start-up, the gas pressure should not drop more than 1-1/2” w.c. when the gas valve opens. On high fire, the gas pressure must stay above the minimum inlet gas pressure.
- Combustion Test – If this is an Alpine, a good O2 reading would be 5.2 – 5.5% O2 in high and low fire. This applies to all Alpine sizes and fuel supply (LP or Natural gas). For all other boilers, check the Installation and Operation manual for the combustion charts. Verify the CO ppm is within spec from the charts.
- Check the delta T – Check the delta T across the boiler in high fire with all boilers running. This should be less than or equal to 35°F. We normally like to see 25°F or less.
- Recheck gas pressure – With all boilers on high fire, verify gas pressure stays above the minimum rating.
Joe – Great! Is that it?
Ron – Pretty much in a nutshell. If this is an Energy Management System (EMS), check the Installation & Operation manual for set-up. I slightly touch on this during our first meeting. Remember, you have two options when using an EMS. Run a boiler enable (T-T Demand) and a 4-20mA signal to the master boiler and let it control all the others or run the same demand to all the boilers and let the EMS control each individual boiler.
Joe – Sounds good, Ron. I don’t believe I have any other questions. Wait! I just thought one! If the master boiler fails, do the slave boilers still continue to operate?
Ron – That is an excellent question. Yes or no depending on wiring. If the EMS is operating each boiler independently, there will be no change due to the system not being set up as a master/slave. If we have a boiler demand wired to the master boiler and Cat5 cables between all boilers, you can put a jumper on all the slave boilers. When the master control is operating, the slave boilers will ignore the T-T or boiler enable/disable jumpers. If the master control completely fails, the slave boilers will automatically fire as independent boilers using the boiler supply sensor limit until the master control is replaced.
Joe – Got it! Thanks for all the helpful information! Okay, Ron, I have no more questions.
Ron – You’re welcome, Joe. It’s been fun doing this question and answer session with you. If you think of anything else, please do not hesitate to 866-684-1463.
Ron Beck is Outside Technical Advisor and Manager of Training for U.S. Boiler Company, where he’s been since 1998. Ron’s 34 years of experience in the heating industry include climbing the ranks of aHVAC company, from apprentice to service manager. Ron can be reached at: RBeck@usboiler.net
Did you miss Ron’s prior interview sessions with Joe the Contractor? You can locate them below!