Delayed off relay/circuit for circulation pump

Piwoslaw · 08-24-11, 02:58 PM

Is there a simpe way to delay the turning off of a circulation pump?

My boiler has only two options for the circulation pump's operation - either always on, or only when the burner is on. I'd like it to keep going for 5-10 minutes after the burner shuts off, so that the heat in the plumbing keeps getting distributed, but I don't want it to run 24/7. I've seen a few relays with adjustable time delay, but they seemed complicated/expensive and I thought that it could be done in some other manner.

Any ideas?

Daox · 08-24-11, 03:27 PM

Another way to handle it would be to use a thermal switch of some sort since what you really want is the pump to be on while there is still warm water in the pipe.

Xringer · 08-24-11, 07:12 PM

My circulation pumps (from forced hot water /oil heat) turn on when
one of the thermostats calls for heat.

The closed contact on the thermostat pulls in a relay (using 24VAC) that connects 120VAC to the pump.

Seems like you could select the "always ON option", and insert an SSR in series with
the AC going to the pump. Then, you could easily control SSR using 3 to 15 DC
control voltage from a thermostat or a simple 555 timer circuit..

555 Timer Operating Modes
Monostable mode.

Piwoslaw · 08-25-11, 12:37 AM

The thermal switch is a good idea. I'd wire it in parallel to the burner/pump signal, to make sure it turns on when it should.

08-24-11, 02:58 PM	#1
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	Delayed off relay/circuit for circulation pump Is there a simpe way to delay the turning off of a circulation pump? My boiler has only two options for the circulation pump's operation - either always on, or only when the burner is on. I'd like it to keep going for 5-10 minutes after the burner shuts off, so that the heat in the plumbing keeps getting distributed, but I don't want it to run 24/7. I've seen a few relays with adjustable time delay, but they seemed complicated/expensive and I thought that it could be done in some other manner. Any ideas? __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

08-24-11, 03:27 PM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Another way to handle it would be to use a thermal switch of some sort since what you really want is the pump to be on while there is still warm water in the pipe. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

08-25-11, 12:37 AM	#4
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	The thermal switch is a good idea. I'd wire it in parallel to the burner/pump signal, to make sure it turns on when it should. __________________ Ecorenovation - the bottomless piggy bank that tries to tame the energy hog.

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08-24-11, 07:12 PM	#3
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	My circulation pumps (from forced hot water /oil heat) turn on when one of the thermostats calls for heat. The closed contact on the thermostat pulls in a relay (using 24VAC) that connects 120VAC to the pump. Seems like you could select the "always ON option", and insert an SSR in series with the AC going to the pump. Then, you could easily control SSR using 3 to 15 DC control voltage from a thermostat or a simple 555 timer circuit.. 555 Timer Operating Modes Monostable mode.