Boiler temps low during off cycles for DHW

bruce pirger

Summer if here and my Buderus boiler is only firing to make DHW in my indirect (Megastor 52 gallon). The tank is great, and without a hot water demand (i.e. all day) it only requires heating maybe once a day. During that time, the boiler temp drops very low...basically to ambient...about 75 degrees. Does this constant temp swing casue problems?

Boiler is the smaller G28 (can't remember exactly the model anymore...bummer.) 60K BTU/HR. The control is a Tekmar 363 which also controls the floor radiant with variable speed inject (in WWSD now).

When there is a DHW call, the primary loop circulator turns on, as well as the DHW loop pump. This pump turns on immediatly with the DHW call...which cools the indirect some of course...but basically it goes into warm up the primary loop, so it isn't all lost. I believe the 363 can be told to make sure the primary loop is at a minumum temp before turning on the DHW pump, although I think this option is not true when using the primary loop pump controlled by the 363 as well.

Anyways, the question is...

Am I causing damage to my boiler by allowing it to fire this way? 75 to 160 everytime it fires basically...all summer long...

Thanks.

hydronicsmike

Nope!

Condensation is only an issue if it occurs over a longer period of time. When a call for DHW comes in and the Boiler is cold, you may get some condensation while the boiler is coming up to temperature. But once the temperature raises above the condensation point, any condensation occured up until that time, will burn off.

If I am not mistaken, the condensation point is around 127°F??

I hope this answers your question. Regards,

Mike

Joe@buderus

Buderus Boilers are designed as a cold start boiler. It is recommended to have the water in the boiler to reach at least 125 degree's per burner cycle.

The Buderus Logamatic Control has a feature where the DHW circulator will not be energized till the boiler water temperature is above the DHW tank temperature to prevent the reverse heat transfer. I would suggest consulting with Tekmar to see if it is offered on their control. Tekmar - 250-545-7749, Buderus 1-800-283-3787.

bruce pirger

Thanks for the info gentlemen.

As an update, the new post purge relay control has been operating perfectly now for about 7 months. Looks like, knock on wood, the problem has been fixed.

Thanks!