tempering cold return water from zone

[mark schofield]

I've been monitoring the temps and preasures on a new WM WTGO3 boiler 3 zone baseboard Taco 007 pumping away primary loop only. All goes well as explained in Dan H's book. However, on a call for heat, for the first 45 seconds to 1 minute, the return water into the boiler will drop to room temp and then heat up to 15 to 20 degrees below supply temp and remain that way until the circulator shuts off. This will happen with a call from any single zone or a combination. No longer than one minute. I had plumbed 2 extra Ts to use for a future zone, and a few days ago used them for a bypass loop to direct hot water back into the return to raise the temperature of the return water. I put a ball valve in the middle of the loop - about 3 lf - and opened it enough to keep the return water at a minimum of 125 for the first minute. The heat from the radiation has remained the same and the preasure differential only changed (dropped) .5 psi between supply and return. I would like to install a mechanical 3 way mixing valve if possible which would modulate with the drop and then rise of return temperature. Something lihe a Honeywell AI102R or a similar Taco unit, but I am not sure that they would suit my application. The ball valve is working fine, but it doesn't seem too profesional: and because it will always send some hot water back into the return, short cycling might occur as the warmer weather approaches and the load diminishes. And to keep it simple, I would rather not get into motorized valves and their controls. TIA for any suggestions.
Mark S.

[firecontrol]

The amount of time that the water is returning to the boiler at room temperature is not a problem as I see it. Surely not enough to justify the amount of added complexity that you're suggesting.

[johnsp]

Yea, don't go nuts for 1 minute of low temps. Once you get back over 140° you'll dry off any condensation real fast. This would be expected behavior with any cold start application.

[mark schofield]

thanks for the replies. this isn't a cold start situation. the boiler has a tankless coil for DHW so it stays on all the time, mostly hovering around the low limit and it's differential. 170hi/140lo