View Full Version : Boiler pump question

09-18-2009, 10:12 PM
I'm wiring a boiler for a plumbing/heating contractor- Lochinvar 150.

What will happen if boiler pump is made to come on along with DHW pump when DH stat calls for heat?

09-19-2009, 09:01 AM
Depends on how it is piped. If it is primary seconday, as most copper tube boilers are, and the DHW tap & pump is off the primary, the pump must run.

09-19-2009, 09:40 AM
There are four zones and the set up matches the description in the manual calls this "zoned with valves".

There is a picture on the next page called "non-zoned primary/secondary". The DHW looped is plumbed the same in both.

The DHW loop on the boiler in the house is plumbed off the primary I believe.

Check me on my terms-boiler loop/boiler pump is the primary.
Individual runs to room heat, supply/return manifold, system pump is the secondary?

My questions are to satisfy my own curiosity.

If the boiler pump must run on a call for DHW why does the unit come pre-wired to switch the boiler pump off and the DHW pump on?

09-19-2009, 10:30 AM
In a primary/secondary configuration, the heating zones normally come off the secondary loop. The primary loop may or may not come on to provide heat to them, and may be controlled by the high/low boiler controls - the primary loop would only come on when the boiler was on (and may remain on to purge the heat exchanger for a bit), while the secondary loop would run whenever a thermostat called for space heating (they may not both always be on).

But, when the DHW calls for heat, assuming it is on a priority zone, you'd want to fire the boiler (which would cause the primary loop pump to turn on) and turn off the secondary loop to allow all of the heat to get to the DHW. the goal is to reheat the DHW as fast as you can, whereas the space heating may not want or need that high of a fire rate, and the heat in the secondary loop may be sufficient. To ensure you get max heat to DHW, you turn on the primary, and off the secondary, then max heat is available to DHW production.

09-19-2009, 01:50 PM
This boiler runs the system pump if a room stat is calling for heat, when boiler fires either boiler pump or DHW pump will run but not both. DH has priority. DH loop is tied into primary.

The installer wants the boiler pump to run every time the boiler fires as you two are describing but that is not the way the circut board inside the unit is configured. What am I missing?

09-19-2009, 05:03 PM
i have lochinvar 105 w indirect, also.
I believe the circuit board expects the dhw pump to be in series w the boiler and the indirect, and therefore the dhw pump will give the boiler all the flow it needs.
or, if no dhw call for heat, then the boiler pump supplies the boiler,

that is, one , or the other, will supply the boiler what it need,No point in running both.
Ck. the lochinvar install manual, it's all spelled out there

09-19-2009, 05:08 PM
That's the way I see it and the manual explains it that way too.
There must be something special about Lochinvars that differs from other condensing boilers.

09-19-2009, 06:28 PM
I looked at the I&O manual, and and it is clearly primary/secondary. Its just that the DHW circ pulls off the primary circuit, thus the DHW circ does not create flow through the boiler. The boiler circ must run, as these boilers need constant and consistant flow.

09-20-2009, 04:34 PM
My I and O manual gives you both options:
p/s, with dhw operating as a zone,
alternatively, you can pipe the indirect right off the primary circuit, with a Tee . That has either one pump or other running, and that gives DHW priority over space heating