First post, thank you for the incredible resource you provide here. What a place for answers!
- Bosch Combi 151 ZWB42-3A using LPG
- Combi internal circulator ([email protected]~20'-0')
- Grundfos 15-58 FRC circulator ([email protected]'-0') with three speeds
- Braeburn programmable thermostat
- Taco single zone controller sending demand to combi and controlling Grundfos pump
- Outdoor reset is not installed
- Supply pipe temp sensor is not installed
- Rough estimate of H[ft] is 9.06 (~151' of pipe X 1.5 X .04)
This is new construction single level 1100sq-ft ranch modular with the boiler install completed in the hottest summer months. Heat is sent into a single zone to baseboards with what seems to me to be a standard primary-secondary setup. The spacing on the tees is not the recommended less-than-or-equal-to 4", but 6" to 8". The installer did not use the Bosch controls (his words for not using the Bosch CRC200 and outdoor reset, and why he used the Taco instead were that a small system like this doesn't need "all that."). I am struggling to determine the cause of my problems in gaining heat in the home now that the cooler months are here in the northeast. My loop has been twice-bled (hose from return drain into a 5g bucket), so I think air blockages are out. All baseboards get warm, even hot, sometimes, but not enough heat transfer is occurring. We have a kick-space heater in the kitchen, and if I turn that on, there is a very noticeable improvement. Trouble is, it's optional, and it's somewhat noisy. We are hoping it isn't required.
- Nighttime set point of 64F
- Morning set point of 67
- Afternoon set point of 64
- Evening set point of 69
When I wake up, roughly 45 minutes after the morning set point engages, the temperature in the home is still 64 degrees with 28F outdoor temperatures. A look at the boiler LED shows the temperature swing from 140F to +/-190F. When the boiler turns off, the temperature drops about a degree every two seconds, slowing down over time. When fired back up, the temp climbs strangely fast, making me wonder if the system is not pulling water through the boiler, and its hot water sits going between the supply and return through the unrestricted tee.
This past weekend, with the first dip into the twenties, we tested without the kick-space blower on and found that from 64 to 69 took five hours.
Further examination led me to use tape on several points of copper and PEX and use my IR thermometer to gauge actual system temps. During firing, in order of exit from the boiler:
- A - Copper Supply line as it exits boiler - 170
- B - Copper Primary line just downstream from 1st tee - 169.5
- C - Copper Primary line on other side of expansion tank and air vent - 169
- D - Copper Primary line 10" above Primary circ pump - 169
- E - PEX Primary line 20' away - 147
- F - PEX Halfway point of loop - 145
- G - PEX Primary line 20' away on return - 135
- H - Copper Primary return ~4' away from return line to boiler - 172
- I - Copper return line 3" from entrance to boiler - 172
- K - Copper common pipe between supply/return - 172
It's not easy to take all these measurements and record them, all while the boiler is running, so there may be some room for error there. The takeaway for me isn't that the return is sometimes hotter than the supply, although that seems pretty obvious too, but that 20' upstream, it is 40F cooler.
I now realize (having watched extensive YouTube videos and read several blog posts and other documents on old-school expectations of new condensing boilers) that I may need to change the way I think of a heating system regarding setback at night and during work hours, but I still feel that something is off here.
My main questions:
- Can this boiler work without the primary secondary setup?
- If not, is the tee spacing critically important? - it is not what the manufacturer recommends
- Is gravity circulation a possibility?
- How fast is too fast for a boiler temp to climb running at a claimed
- How fast is too fast to cool off?
- Is there a rule of thumb for pump speeds, like integral low/primary high?
- Is the CRC200 a better fit for this system than a simple thermostat switch?
- What is my next step?
If you made it this far, I thank you very much. I can't believe I wrote this wall of text. I look forward to hearing from some of you with your ideas and tips.
Pics and some extra info below