Can HydroStat 3200+ be set for WWSD in Summer w/o ODR sensor?

D107

@Harvey Ramer New atmospheric boiler install with Turbomax Reverse Indirect, Hydrostat 3200+ DHW priority. Not sure if Hydrostat can achieve WWSD without ODR sensor which we don't have and likely wouldn't use otherwise.

I'm trying to avoid having the boiler --even if all thermostats are off--fire up on low limit all summer because 'it thinks' heating is still on. As set up now, the tank aquastat will turn DHW circulator on when tank temp gets below 140 and turn circ off when tank temp reaches 150 of 160 depending on how we set it. The boiler will and should fire on and off between the its lo and hi limits (140-160) to maintain tank temp. or perhaps I could change boiler limits also to 140-150 as long as return temps from DHW won't get too low.

Without WWSD there could be situations in summer where, certainly overnight or after morning showers, and tank reaching high limit again, dhw circ goes off, little or no hot water is used for the rest of the day, the tank retains its temp above the low limit but the boiler water goes below its low limit and turns on the burner--not the heating circ/zone valves since t-stats are off--so now I'm wasting burner firings to maintain boiler heating limits when there's no DHW demand. If there is a way to set WWSD then that might take care of this(?)

HVACNUT

You absolutely need ODR to utilize WWSD.
Why cant you turn the low off?

D107

@HVACNUT & @Robert O'Brien If you mean turning the boiler low limit off that would work to suspend summer heating, but I thought the boiler LL had to be kept to handle the dhw priority. If the tank hit its low limit and starts the circulator, what would tell the burner to kick in to start raising tank temp? I'm sure I'm missing something.

Robert O'Brien

Why not just turn LL off and have cold start?

D107

Spoke with hydrolevel, they agreed about turning LL off and added that via slightly different wiring the aquastat could be set up to both turn burner and circulator on. Will have installer speak directly with them. Hopefully our particular aquastat can do this. Setting would also have to ensure protection from low return temps.

HVACNUT

There have been cold start gas boilers since time began.
If the Turbo max is set to 150° limit, the boiler aquastat to 160° limit and mixing valve to 120°, there wont be an issue if the pump is correct. I have yet to have anyone tell me there's insufficient hot water with a Turbo max 23 and cold start.

D107

This is a Turbomax 45, 23 probably would have been better suited. So far, even without settings finalized we never run out of hot water. Got it on the remove LL for boiler. Presumably it's ok to keep the low limit on Turbomax (140?). The Ranco aquastat has a minimum 10º differential--from the 150. DHW calls on 140 tank temp.

I've been told that this setting --LL off--can be used for heating season as well. Hydrostat 3200+ has a 'high limit differential' which may protect the boiler. Though I don't really understand the difference between having, e.g. a 20º differential subtractive from 160º hi limit and having a 140º low limit but I'll get it in due time.

Main thing is to do what my mother's Buderus Logamatic did in WWSD in summer and only fire boiler for DHW. So I understand that having and ODR set to WWSD would not be necessary with the settings you have described. Thanks for your and Bob's help.

D107

PS Note that my understanding had been that the low limit was set to protect boiler from low return temperatures--there is no thermal bypass or thermic return valve.

HVACNUT

> @D107 said:
> PS Note that my understanding had been that the low limit was set to protect boiler from low return temperatures--there is no thermal bypass or thermic return valve.

You are correct. In order for the flue gasses stay above its dew point, return water temps should not be below 135° to prevent condensing of those gasses.
But that (IMO) is for atmospheric oil fired boilers.
Like I posted earlier, cold start, cast iron atmospheric gas boilers are a byproduct of the Big Bang. Thousands, dare I say Gajillions are still in service today.
And (again IMO) even on today's oil fired boilers, with much cleaner combustion, and ULSD fuel, a cold start with ODR is a no brainer.
Europe doesn't fire their boilers unless there's a damn good reason.
The 3200 is also a triple acting aquastat, which like you stated, maintains a minimum boiler temperature. The Low limit can be used in applications where the boiler has a tankless coil for domestic hot water so there always needs to be temperature in the boiler. Using it as a triple will also shut off the circulator, should the boiler temp drop to the Low limit, thereby leaving (hopefully) enough temperatures in the boiler for domestic use if needed.
And of course you're using the Economy and Thermal pre-purge functions. Right?
And if you are still concerned, you can use the circulator hold off function to do just that. Holds the circ off until boiler temp reaches 125°
BTW, you never mentioned the brand and model boiler. Did the 3200 come with?
Do the ODR. Whattaya gotta go through granite to get a wire to the north side of the house?

D107

This is a Peerless MI-03, atmospheric. Yes 3200+ came with. Reverse Indirect is Turbomax 45--should have probably gotten the 23--kind of huge for 70kbtu firing rate, 58 DOE, 50 net. 38kbtu heat loss.

Not sure why low return temps is only an issue for oil-fired boilers, never heard that. Hydrostat does play with some pretty low return temps on circulator hold: circ runs at 125º, then won't stop until temp drops to 115º. Anyway we've accepted that.

Using pre-purge but will wait until heating season to try Eco function, which can start as low as 145 target temp. With a ∆T of 20º, that puts return temps at 125. Two zones are cast iron, so lots of cold water coming back on a heating cycle start, especially in shoulder seasons. House is decently insulated--no heat calls in a few weeks.

Ha, no granite nearby. Installer not convinced ODR will work here due to need to keep boiler 160-140. I wanted it also to allow WWSD, but from what you and Bob say seems like removing the boiler low limit will accomplish WWSD--firing boiler only on DHW call in summer. Originally turbomax was going to double as a buffer but that was changed to only indirect. 3200 also has a 'Thermal Targeting'--kind of indoor reset available to use as well.