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[MTJAG]

Just wanted to see if others are having or have had this same problem.

My indoor propane boiler comes on and runs for about thirty seconds when there is a call for heat.  I have the water control temp on the propane boiler set at it's lowest setting of 140 degrees.  It did it again early this morning, so I went down stairs to check it out.  My indoor temp from the OWB on the supply side was at 172 degrees.  The indoor propane boiler shut down after a few seconds and the pumps for the floor heat continued running as normal....just can't figure out why the propane furnace has to come on, when there is ample hot water coming in from the OWB.  Also check my supply pump at the OWB since it is a Grundfos Alpha variable pump to see the flow rate.   This morning, the flow rate was 3 GPM.  I can increase that if need, but again, the lines inside the house were showing 172 degrees going into the heat exchanger....anybody got any ideas?

[mikenc]

Any reason to leave it on. I turned mine off. Hasen't ran in 2 years except  to make sure it works a couple of times.

[fireboss]

What are you using to check the temp? I am finding out that the inferred or the lazor  readings are not accurate !

[MTJAG]

I could turn it off I suppose....just left it on in case I was gone and the wife ran out of wood. 

The thermometer is taped to the return line while the OWB thermomter is an inline type where the probe is actually in the water flow.

[yoderheating]

You need a aquastat on the supply line, that will solve the problem. 

[Dean186]

Hi MTJAG,

This can happen if your heat exchanger is undersized or if the setting on your inside furnace is not set at its lowest setting.  When a zone has been setting idle for sometime and then starts, it is sending cool water back through the exchanger.  If that water is not heated by the heat exchanger to a temperature above the indoor boiler set point, then the inside boiler turns on.  Once the cooler water is out and heated water is circulating, the furnace shuts back down.  This usually takes the amount of time you have described.

[MTJAG]

Dean,
Thanks much.  That makes perfect sense.  I have the furnace set at 140 degrees which is the lowest setting.  Since I want the propane backup, I suppose I can live with a little run time in temperature transition...thanks again!

[MTJAG]

Thanks for the idea...believe I will do the same.  In the case of my Rinnii DHW, I just turned it off, so it's no longer a problem.