I’m looking for expert advice on what may be the cause of my problem and suggestions on what to do to resolve. I have a 4 ton Waterfurnace Series 7, vertical, closed loop system (more details on the ground loop to follow) installed in a 2625 SQFT home. In the coldest days of winter, I’m experiencing repeated E5 - Frze Detect FP1 errors which typically result in a system lockout and switchover to emergency heat. The system was installed in 2014 in Southeastern, Pennsylvania. The system performs very well in warm weather and cold weather except when we have repeated days where the mean/low temperatures drop into the teens and single digits (Fahrenheit). We experienced 124 of these E5 errors during the 2014/15 winter. When this problem first started, the installer worked with the WF engineers and decided to look at changing the glycol/water (I believe it is glycol based) ratio in the loop suggesting that the installer had used too much glycol thereby reducing the heat transfer capacity of the system. Additionally, the single, variable speed ground loop pump was set to a fixed, high flow rate to increase the turbidity in the loop. On making these changes, things got markedly worse in terms of numbers of E5 errors in the weeks after. The theory then was that air was inadvertently injected into the system during the rebalancing of the glycol/water ratio. On next attempt at repair, the loop was primed again with a larger pump and it was believed that, in fact, air was removed from the system. However, by the time this work was completed, the heating season was nearing its end and temperatures rose consistently into the 20’s and higher and so it was unclear whether this action had any real impact on performance. Now we are experiencing the first significant, prolonged cold weather of the 2015/16 season and the problem has reoccurred. The ground loop is made of 4 loops of 1" piping consisting of 11 total bores of varying depth as follows. The nomenclature below is: Loop # / # of bore holes / individual bore length summed for total length of loop in ft. Loop 1 / 4 / 60+50+50+40 = 200’ total Loop 2 / 3 / 70+50+70=190’ total Loop 3 / 2 / 95+90=185’ total Loop 4 / 2 / 90+95=185’ total The reason given for the odd setup was related to the challenges met when boring in our heavy clay. Water was entering the bore holes as early as 20’. It is my belief based on talking to the drilling sub-contractor, that little casing was used, but much more grout was used than anticipated. To reiterate my goal, I’m looking for expert advice on what is causing my issue. It is my belief that the ground loop does not have enough capacity which could be either due to an under-sizing issue, a configuration issue with the unusual number of bore holes looped together, or some combination of both. My plan is to continue to work with the installer to get resolution. To date, they have been very responsive and have been in the HVAC business for long time in this area. I’d also like to have opinions on what might be an acceptable solution. e.g. increase length of existing loops, add a fifth loop, start over and re-drill, etc. Thanks in advance to anyone willing to help.