Bosch Greenstar Combi 151 ZWB42-3A

rocksolidsr

I recently installed a Bosch Greenstar Combi 151 ZWB42-3A boiler along with a radiant heat setup and I had a few questions that I was hoping you guys here could answer.

1. I turned on the ECO mode and was curious what exactly that did. I thought it would turn off the circulator pump when heat wasn't being called but it was still be circulated.
   
2. When the thermostat calls for heat the boiler is actually firing 42% of the time and when the thermostat is not calling for heat the boiler is actually firing 4%, does that seem normal?
   
3. When the thermostat is not calling for heat the pump in the boiler is still running and is maintaining the primary loop but is that really necessary? Is there a way to only run the boiler pump when the thermostat is calling for heat?
   
4. When installing this system I had a heck of a time tightening the 1" copper supply and return lines to the boiler without leaks, there is still a small leak on both supply and return, it seems as though the fittings on the boiler were not NPT but rather straight and did not make a seal, is there a special fitting I should be using against the supplied fittings in the boiler?
   
5. When it finally heats up here in North West PA I was planning on redoing those leaky 1" supply and return lines but I also use the boiler for domestic hot water, can I turn off the radiant heat and service those lines while still using the DWH?
   
6. I am planning on adding two more zones but I'm unsure of how exactly to control it. I have a valve on the supply and return to hook into just not sure if I can use the pump I already have or if I will need another one or what?
   
7. I used to heat with a furnace and heat water with an electric hot water heater and now that I've switched to the boiler for everything it seems as though I am consuming a lot more propane which I expected some because of the hot water but I didn't think the hot water would cause that much usage. I usually have to fill my propane tank twice per year and this year will probably be three times.
   
8. If I decide to switch back to my electric hot water heater do I need to do anything on the boiler or just shut off the supply water?
   

Thanks for any help

Ironman

Just looking at your pics: that's not piped correctly. When using closely spaced Tees to achieve p/s, one circuit MUST flow straight through the run of the Tees and the other MUST flow through the bull (side) of the Tees. Plumbers, for some reason, have the hardest time accepting or grasping this concept.


The flow in the primary is from left to right in the diagram. Either circuit can go straight through and be considered the primary, but it should be the larger one.

You also need to use the system sensor (item#14) with that boiler:

rocksolidsr

Why is the system sensor required? I do not have the CZM100 controller so I don't have anything to connect it to.

One other question I had was do I need the FW 200 in order to use the outdoor reset control (i.e. outdoor temp sensor) or can I just hook up the outdoor temp sensor?

Ironman

Uh, did you read the I/O manual closely? The system sensor connects to the Heatronic control board if there's no CZM100 used. You need it because the manufacture says so.





If you want Outdoor reset, then you have to use the FW200. If you want Indoor reset, use the CZM100 with a CRC 100 or 200 indoor sensor and not the FW200. If you use IDR, then remove your present t'stat and the honeywell pump relay and use the CZM 100 and the indoor sensor.

You'll probably have short cycling issues during space heating because the connected load is far smaller than the boiler's minimum output (4 loops of 1/2" pex @.75 gpm each = 3gpm or about 15k btus on a radiant floor). Minimum boiler output is 31.7k on natural gas, 42k on LP.

rocksolidsr

That graphic says "optionally connect". What function does that sensor do I have read the manual and it doesn't state what it is needed for or even that it is required? My boiler did not come with that sensor so I did not think it was required?

What does short cycling look like, is there a way I can determine if my system is doing that? My system does have 4 loops of 1/2" pex each about 200-250' in length.

In terms of the primary/secondary would the picture below be the correct way to pipe it?

Ironman

It's says "optional connection" because that's where you connect it if you don't have the CZM100. It doesn't say the sensor is optional.

The only time the sensor is not required is when the space heating loop is small and can be directly pumped by the internal boiler circ. You can't do that with your radiant floor setup. It has to be piped p/s.

The purpose of p/s piping is to achieve hydraulic separation. That simply means that each circuit can maintain its own flow rate will mixing in the common piping between the closely spaced Tees. The flow rate and water temp in the boiler loop will be different than the flow rate and water temp in the radiant loop. For that reason the sensor is needed to tell the boiler what SWT is going to the floor. That's also why the placement of it MUST be as shown to get a correct reading.

This is also why the delta T circ that you have is not a good choice for you system: as it varies speed to achieve its set point, it will confuse the logic of the boiler. It's the boiler, with either its IDR or ODR that you want to control the water temp in the floor. This is the way to get the most comfort, economy and longevity from your system.

The way it's setup now with no Reset and the delta T circ is fraught with problems and making the system far less efficient and comfortable than it should be.

With a radiant floor, the FW200 control with a properly set ODR curve is the way to go. The control is very smart and has adaptive logic which will compensate even if the ODR curve isn't ideally set.

And yes, your markup looks correct.

Noel

Only the FW 200 looks at the system sensor when connected to the boiler. With the CZM 100, the system sensor connects directly to it on terminals TO. With the floor boilers using a CZM 100 panel, the system sensor leads disconnect from the boiler control and connect to TO in the CZM 100, and the boiler control would need to be reset (function 8.E). Otherwise, you wouldn't need the system sensor, which is why it doesn't come with the CRC 200.
Noel

rocksolidsr

I called tech support and asked for the external supply temperature sensor (8 737 700 289 0) and they said that I can only use that if I have the FW200 installed as well.

If I were to get the FW200 would the thermostat still be controlling the temperature of the room and the FW200 only controls the temperature of the water?

Since I'm not using the FW200 currently does that mean when the burner is on it is always 100% or does it modulate based on the internal water temp?

Does it make sense that the internal circulator pump is almost constantly running? Would fixing my p/s piping fix this issue?

Do you recommend a different 1" female NPT to connect to the boiler to help fix my leaks?

Ironman

Yes, the t'stat can still control the room temp; however, if the ODR curve is dialed in right, the stat becomes unnecessary. It just becomes a type of "high limit" for room temp.

The ODR function adjusts (resets) the supply water temp based upon outdoor temp. The colder it is outside, the warmer the supply water temp and vise versa. This greatly increases the efficiency of the boiler while actually being more comfortable.

The boiler will modulate and attempt to run as long as possible on as low of a fire as it can. This is the most efficient approach, but Americans have a hard time grasping it because we're used to bang , bang technology - 100% on; 100% off. The lower the RWT, the more efficient the boiler is operating.

P/S will correct a lot of issues, but not the micro zoning that I previously mentioned. Adding more loops and/or a buffer tank is the solution for that. This is the big issue with combi boilers: in order to size it sufficiently for the domestic load, it's almost inevitably way too large for space heating. This is why a properly sized boiler plus an indirect is the better choice, but folks will grab for the combi because of its lower initial cost.

I'm not sure where your leaks are, but if it's the threads at the boiler, then several wraps of good Teflon tape such as Blue Monster plus Teflon paste will fix it. Copper unions are notorious leakers: Teflon paste carefully applied to the mating surfaces usually works to stop leaks there.

rocksolidsr

Thanks for all your input I really appreciate it!

Noel

The thermostat still controls room temperature, the FW 200 only controls water temperature. The boiler pump runs for freeze protection all winter, and in mild weather there is a pump post purge time after a heating cycle ends. The boiler will modulate its firing rate all of the time based on load, even at constant temperatures. The dial setpoint is the temperature it tries to modulate at, the limit setpoint is 10°-20° higher than that number.
The outlet piping in the U.S. bracket is NPT, no gaskets under it are needed. The bracket to boiler connections all require the included gaskets above the bracket.
Noel

rocksolidsr

Would it be possible to use the CT 100 thermostat/controller with my setup?

I've read the manual but can't seem to figure out how I would control my system pump using the CT 100.

I am planning on adding 1 more loop to the current zone and then adding two more zones that should help with the load right?

Noel

The CT 100 is a stand alone, single zone, constant circulation control, as is the CRC 200.
For multiple zones, the CRC 200 and CRC 100 controls can be used with the CZM 100 panels, controlling up to 8 zones.

rocksolidsr

In the brochure for the CT 100 it says it can control multiple zones "Can I use the Bosch Control
to control more than one
zone e.g. more than one
heating zone?
Yes, the Bosch Control is able
to control multiple zones with
standard non-Bosch zone
controlling systems."
prowaterheatersupply.com/PDFS/Bosch_Greenstar_CT100_Smart_Thermostat_Brochure.pdf

Any idea what they mean there?

Noel

It is a mistake that I hadn't seen before. The CT 100 is a 14 volts DC control that transmits data; it isn't an open/close switch type control. Bosch calls this class of controls "Bus devices" and they only work with specified boiler controls, as listed on that webpage. Only one bus device can be used on a boiler, not a combination of them. One FW 200 or one CZM 100 panel system or one CT 100 or one CRC 200 without a CZM 100.

rocksolidsr

Just out of curiosity how does a system with the CT 100 control the system pump?

Noel

It doesn't. The pump is always running with a constant circulation control.

rocksolidsr

ahh i see! thanks!

rocksolidsr

So I was finally able to fix my leak and correct my primary secondary loop issue.

I would like to add two zones to my current setup and the attached picture is how I'm thinking of connecting/controlling everything, do you think this will work, or am I missing something?

ratio

Why not come off the ends of the existing manifold to feed the new one?

rocksolidsr

if I did that wouldn't I need thermostatic actuators on every loop?

ratio

Isn't that what's shown on your new manifold? How were you planning on controlling the new loops?

If you end up just 'extending' the manifold, you should verify that the current pump has the capability of feeding the added zones. I didn't mention that when I made my suggestion.

rocksolidsr

So in total I would have three zones. I was thinking of leaving the 1st zone (5 loops) I have there alone controlled by the thermostat to the honeywell relay to turn on the pump.

The 2nd and 3rd zone would have a dedicated pump which would be controlled by the end switch of the actuators and each actuator would be controlled by individual thermostats.

Does that make sense? That way I wouldn't have to get 5 more actuators

ratio

I see. For some reason, I thought the existing manifold had valve actuators on it. Your proposed fitup is less than optimal, but given the existing pipework might be the simplest solution.

No chance of doing the suggested repipe?

rocksolidsr

There is always the option of redoing! What would recommend then, extending the manifold and have 7 total actuators? I would be concerned the signal pump would not be able to hand all of that load if all zones called for heat at the same time

ejabbo

I am going to start a new post. Couldn't delete my follow up question to this post. I am having a bunch of problems with a new install of a Bosch Combi 151 ZWB42-3.

I hope your situation has been resolved.

PatrickHennessy

I am installing the Greenstar 151 in 2 weeks and getting all the info I can on it. I keep hearing about "short cycling". How can one tell if the boiler is short cycling? Thanks..

nicholas bonham-carter

If a boiler which is too large for the building heat loss is installed, then the boiler will start and stop as it strives to maintain the temperature set either by the outdoor reset, or the thermostat. The first thing to do is to calculate the heat-loss of the building, using software, like the SlantFin app.
The most efficient setup has the boiler running constantly on a design temperature day, as it’s output closely matches the heat-loss.
If you are stuck with an oversized boiler, then you can partially compensate for the mismatch by installing a buffer tank to make the runtimes longer, however the best thing to do is choose the right sized boiler to begin with.
This is often the problem with Combi boilers-sized too large to make hot water.
An indirect hot water tank on a smaller boiler would be a better choice for efficiency, and equipment longevity, as the heat exchanger will not come into contact with the impurities dissolved in tap water.—NBC

markman77

Anyone ever answer the question:

1. When the thermostat is not calling for heat the pump in the boiler is still running and is maintaining the primary loop but is that really necessary? Is there a way to only run the boiler pump when the thermostat is calling for heat?”