Circulator hold off

Evan0307

My new Lennox boiler has an optional feature called the Circulator hold off, where it will wait until the boiler reaches at least 125 degrees before activating the circulator to reduce the possibility of the boiler condensing. Currently my boiler is under the factory settings so I am wanting to activate this feature this weekend. My question for the group is if there are any disadvantages to activating the circulator hold off feature? To me it seems like a good idea but I since it is an "optional" feature and not a standard setting I am assuming there must be pros/cons that go with it? Any advice is appreciated thanks!
P.S. This is a gravity system converted to a boiler with circulator.

STEVEusaPA

It's a good idea in general. The reason why it's optional is because you could pipe your boiler primary-secondary, or pipe it with a mixing valve to protect your boiler. In both of those cases you probably wouldn't need it.

Evan0307

STEVEusaPA said:

It's a good idea in general. The reason why it's optional is because you could pipe your boiler primary-secondary, or pipe it with a mixing valve to protect your boiler. In both of those cases you probably wouldn't need it.

Ok thank you. Since I am not aware of a mixing valve I would guess I do not have that! Makes sense.

EricPeterson

My boiler (Burnhan ES2) does not have this feature AFAIK, but I have thought of installing an aquastat to achieve the same purpose - i.e. hold off running the circulator until water reaches a certain temperature.

If I do install the aquastat, the best place to install it would I think be somewhere on the boiler output, what would be the recommended setpoint?

Currently I have a system bypass valve installed that is set at 50% open (returning heated water to the return), but no primary-secondary or thermostatic bypass (hope to add this summer).

I have also thought of installing an aquastat as a fail-safe, where it would shut off the boiler if the temperature exceeded a certain temperature, if for some reason the control board fails to properly manage the boiler operation. Has anyone installed an aquastat for this purpose?

Thanks,
Eric Peterson

DJD775

Depends on your setup. On my old high mass boiler I would use the function as it would spend a significant amount of time in the condensing zone without the circulator holdoff. My new boiler is a low mass, 3 pass, boiler and it heats up quickly so it spends little time in the condensing zone so I do not activate the circulator holdoff. Without the circulator holdoff my runtime is extended which leaves me in the 'steady state' more often.

hot_rod

It depends on how your boiler matches the radiators. If the boiler is oversized and can get above 130F return within 10 minutes from a cold start, that is acceptable, no need for return protection.

Every system is different, observe the operation.

You may fine the circulator bangs off an on a lot with a control like that. Especially if it is a low water content and low mass boiler block. Cast iron boilers have shrunk a lot over the years

I remember the Viessmann cast boilers had the temperature probe in the top of the boiler. It was a multi port well with 3 sensors all in one well.

EricPeterson

hot_rod said:

It depends on how your boiler matches the radiators. If the boiler is oversized and can get above 130F return within 10 minutes from a cold start, that is acceptable, no need for return protection.

Every system is different, observe the operation.

You may fine the circulator bangs off an on a lot with a control like that. Especially if it is a low water content and low mass boiler block. Cast iron boilers have shrunk a lot over the years

I remember the Viessmann cast boilers had the temperature probe in the top of the boiler. It was a multi port well with 3 sensors all in one well.

My system is a converted gravity system so I guess a high mass, high volume setup - nine large radiators and CI baseboard in three rooms.
The boiler is an ES27 with a water content of 5 gallons.
Burnham claims that the minimum return temperature is 110F.
It is not oversized based on the analysis done prior to purchase.

I recall that the original boiler in this house had very primitive controls - it was setup with two aquatstats. One turned kept the circulator off when the water was too cool, the second turned off the burner when the water was too hot.

Eric Peterson

EBEBRATT-Ed

@EricPeterson

The best way to control boiler return water temperature (if it needs controlling) is with a mixing valve.

An aqua stat is not the best way as it can just burn extra fuel and wear and tear on the pump and controls from cycling a lot.

If you have a high mass system a mixing valve is the way to go

hot_rod

Sure enough they show a 110F acceptable return, Wonder how the flue can handle that.
Is any return protection device needed with that acceptable return temperature?
Sounds risky?