Return temperatures have been so deep into the cold area that the pink “control” temperature is almost off the chart. The average return line temperature has been hovering at around just 90˚ and has even fallen as low as 70˚. Would you be happy with “hot” water 28˚ colder than you are?These sample charts tell us important things; the boiler is producing hot water on schedule (that’s good), the drop in return temperature is severe and continuous (that’s bad), and, our resident on the end of the loop (and possibly everyone else) is quietly enduring unacceptably cold water, 15˚ to 45˚ degrees colder than our delivery temperature.
This information narrows things down to two culprits; you either have a bad cross-over problem (cold water mixing into the hot water) or the return line pump is not pulling hot water back to the boiler.
The return pump is the easiest and cheapest to address. Feel it to see if its motor is operating. If it is, and you are still suspicious, call a boiler tech to open the pump and inspect the impellers. Damaged impellers can spin all day and still not pull any water through the line.
Compare the two charts and you’ll notice that the delivery temperature is quite smooth while the return temperature bounces up and down in a jagged irregular manner. If the return pump was dead, there would be little water flowing through the return line and the line would fall to a fairly stable low temperature. But our rapid fluctuations are suggestive of the second and more pernicious problem.
Cross-over, especially intermittent cross-over, would explain the erratic return temperatures and will addressed in a future article. Resolving cross-over issues is an subject to itself.
Run a Hot Water Analysis to see if the problem is chronic before dismissing a transient fluctuation. Low Return Temperature alerts are too often dismissed because 1) the problem is often transient, 2) cross-over is a “plumbing” and not a boiler problem, and, ironically, (3 we lose track of how often they occur and do not recognize that the problem is actually chronic.
The pink areas on the Hot Water Analysis chart indicate every day in which the return line ran too cold. You can see from the calendar that it recurs during cold weather and is getting worse. In this case, our residents took cool showers 14 of the 31 days in January, an unacceptable level of service.