I purchased a home last January and have already spent a bit of money trying to get some of the heating options sorted out. One of the systems was a an outdoor boiler/indoor electric boiler system. I had the wood boiler disconnected for this season since I'll be traveling. While that was done, I had them replace the 12 port manifold with a newer one with flow rate adjustment and add an outdoor reset and slab sensor.
After the new manifold went in, the flow rates have been consistently running around .15 GPM over the 12 loops wide open. The circulating pump is a 1/25 HP Grundfos 15-58FC but it makes no real difference between the medium and high settings. There's an 60kbtu Seisco SH-18 running at the moment and its putting out 120F water and the return is showing around 70F.
Since the pump looked easy enough to swap out, I tried putting a larger 1/6 HP Steibel Eltron CP3S26-110BFC on it this past weekend only to have the end result show the exact same flow rate of around .15 GPM irrelevant of the low/med/high setting on the much larger pump.
I don't technically know what the length or even locations of the 12 zones are within my house other than two of them being labelled for the garage. There was a lot of gunk in the system after the wood boiler was disconnected so it was flushed for quite a while. I've also taken the clean out plates off the boiler and tried to clean them as well as I could as well. Nothing seems to make a difference.
Is the flow rate of .15 GPM with the delta temp a concern? Why wouldn't the larger pump make any difference in the flow rate? When I release all the pressure from the system, and then add the pump (either one of them) back in and then raise the pressure back up to around 15PSI, the initial start of the pump causes a slightly higher flow rate, then by the time the air is out of the system again it seems to have fallen back to the .15 GPM. If I close down all but one of the lines, I can get up to about .8GPM from the larger pump and maybe .8 or .7GPM from the smaller pump equally on any one specific line. Open two lines and it drops to .5 or less etc and then down to .15 with all lines open.
Any suggestions or advice?