heat energy purge benefits by running circ pump a little longer?

PeteA

Just a thought I was having, and I was wondering if any others have ever done something similar.

Is there an easy way to keep the circulator running to squeeze an additional minute or two or 3 out of the water that was already heated by the boiler once it shuts down? Right now most of my systems are single zone and I am using the typical dry TT contacts to control the boilers but I noticed that when the high efficiency combi unit goes into its cool down mode the secondary loop circulator which is controlled by the taco 501 has already shut down and therefore the cool down mode of the combi is being done with the internal circulator running through the primary loop but wouldn't that be better and quicker if it could unload the additional water temp into the secondary heating circuit?
The same goes for my cast iron boiler that I installed, I noticed that as soon as the thermostat says its satisfied at 69 degrees the flame shuts down and then the circulator is shut down, would it be better to have the circulator run an additional minute or two to dump the stored heat back into the house?
I'm thinking some simple fan limit control switch strapped to an outlet pipe above the boiler to just connect in parrel to the TT contact that closes at the 140 but opens at around 120. Something very simple.
Does anyone think this has any value to squeeze the extra heat out of the system and into the rooms while the main boiler is off? The only downside I see is overshooting the overall room temp a bit but isn't that better by having the heat in the rooms rather than having the heat energy you've already built up sitting in the pipes?

Just curious if anyone else has rigged up anything for this purpose and if it was worth it. Here is the page from Grainger of the type of switch I was thinking about.

https://www.grainger.com/category/hvac-and-refrigeration/hvac-controls-and-thermostats/hvac-equipment-controls/heating-controls/fan-limit-controls?filters=webParentSkuKey&webParentSkuKey=WP15138259

hot_rod

Most all the hydronic relays have aa post purge setting. Run the boiler through the switching relay and both the boiler and pump runs. The Caleffi switching relays have a fixed 2 minute post purge.
Cetrainlyyou could wire time delay on break relays into the circuit also.

Steamhead

There are several ways to do it. One thread on the topic is here:

https://forum.heatinghelp.com/discussion/comment/1788675#Comment_1788675?

The Beckett AquaSmart is one particular control that has this function built in. I installed one on my boiler:

https://forum.heatinghelp.com/discussion/176551/nice-job-beckett

PeteA

@Steamhead great info thanks for the links I didn't mention that my systems are natural gas but thank you for attaching both of those existing posts. The first link is exactly what I was thinking but I was trying to do it in a much cheaper way but the aquastat strapped to the pipe in that same post is really easy and will probably be the best way for me to go.

@hot_rod as always awesome information. I took a look at the switching relays you mentioned and they are also awesome although I don't see the post purge feature in the single zone 101 controller. and once I jump up to the next controller it puts me at a price point above the aquastat setup.

Thanks for all of the great feedback as always.

Steamhead

@PeteA , Beckett makes an AquaSmart for gas boilers too.