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Posted by HeatPro on August 22, 2005 at 12:06:54:
In Reply to: Boiler Cycling Too Frequently posted by John Merritt on August 22, 2005 at 11:23:25:
I have a 400,000 output BTU boiler
++ It is nice to live in a 16,000 square foot well-insulated home that would be served by a boiler that size.
: When responding to DHW demand the boiler, being so powerful, kicks in at around 150F but quickly reaches the cut-out temp of 165F. I am presuming it uses the more powerful Stage 2 burning for DHW demand? The boiler burns only for about 15 secs (every 3 minutes). I am told it would be a lot better for its longevity if it burned for longer periods less frequently.
++ If the boiler drops back to 250,000 on the low fire, then it would require about that time to keep the water in the tank within 15 degrees of the control setting.
: 2. I currently have a higher temp on my return floor heating pipes than on the out. Some plumbers have told me that this is impossible, but trust me it is true, and I believe it is being caused by air locks causing the flow to be in reverse - at least past the temp gauge. I have bled these lines but the same problem seems to have emerged. What can cause this?
++ If you don't have a zone valve or a flow control (heavy check valve) on the line, water can be pumped backward through the loop when the circulator is running.
: Are these issues related, or can I do something to minimise the cycle frequency by changing the mix temp/pipe volume/DHW temp?
++ No, they are unrelated.