Weil McLain Eco110 not performing

[jtrolt]

Regardless of how many adjustments I make to the heat settings in contractor menu for this unit, it refuses to exceed 103 degrees absolute maximum supply output. I've gone to all extremes. Of course, Weil McLain refuses to talk to me. Plumber is poorly educated in radiant systems. Insists 90 degrees should be max output, as I'll have hot feet on my concrete slab, and any higher temps could "shock" the concrete. Seriously.
(Back story: This replaced a one year old Takagi tankless, sold to me as part of a Radiant Company system. Before it melted down, it was providing 110-120 degree heat to floor. On a 25 degree day, it would run 1.5 -1.75 hours, satisfying heat demand, then relax for 14-16 hours before needed. Boy do I miss those days. No, I couldn't replace with the same model. You see, Takagi claims the Federal government has now ruled tankless water heaters to be unapproved for closed radiant heat systems. Hence, no warranty. Of course, Radiant company heard all about it from me, but I see 9 months later they are still blissfully promoting this unit for their systems. Idiots.)
So- how do you get this complicated, smarter than you boiler to stop satisfying itself with its little secondary loop for hours on end, drip feeding an average 10 degree rise in temp to my system, and start pumping some hot water? I need 120 to 130 minimum, as that's what my system is designed for.
Is it just a defective unit?

 

[Dana]

Regardless of how many adjustments I make to the heat settings in contractor menu for this unit, it refuses to exceed 103 degrees absolute maximum supply output.

If it's being over-pumped it may not be able to hit higher temps because of limited burner size and/or (less likely) excessive radiation.

Your Takagi (what model number?) probably had more than 180,000 BTU/hr of output, the ECO 110 has about 100,000 BTU/hr.

If your house is similar to 19 out of 20 homes in the Black Hills your heat loss is no more than 50-60,000 BTU/hr, assuming you have some fluff in the walls & attic and glass in your windows, doors that shut, etc.

(Back story: This replaced a one year old Takagi tankless, sold to me as part of a Radiant Company system. Before it melted down, it was providing 110-120 degree heat to floor. On a 25 degree day, it would run 1.5 -1.75 hours, satisfying heat demand, then relax for 14-16 hours before needed.

That sounds like it was being run at a burn rate WAY higher than the heat load, and just using the thermal mass of the slab as thermal buffer to keep room temperatures from overshooting. With modulating condensing boiler such as the ECO 110 (which is probably oversized for your heat load, BTW) you never want to do that, since it's much less efficient than simply setting up the outdoor reset curve so that it runs all the time at lower temp and lowest possible firing rate that still satisfies the loop, which is the recipe for maximum efficiency & comfort.

That's actually a crappy way to run a tankless too and probably why it died in only one year. They last a lot longer running a low flow & lower fire, keeping it under half it's maximum firing rate.

I've been heating my house + domestic hot water for the past 10 years with a tankless Takagi KD20 that has NOT been overpumped and NOT been overfired. The maximum output is about 155,000 BTU/hr, I've never run it at more than ~65,000 BTU/hr, which it somtimes hits when someone is taking an endless shower during an extended call for heat. My 99% design heat load is about 35K, but with the radiation I have I can emit about 45K, and I have it set up to deliver that at a flow of no more than 2-3 gpm through the tankless (the radiation flow rates of all the zones add up to about twice that), taking advantage of the tolerance tankless heat exchanger have for large delta-Ts, a tolerance that modulating condensing boilers do not have.

Simply swapping in a mod-con into a system that had been served by a tankless isn't likely to work well. It needs some pretty basic pumping re-design, if nothing else, but a full system design review would be in order.

So- how do you get this complicated, smarter than you boiler to stop satisfying itself with its little secondary loop for hours on end, drip feeding an average 10 degree rise in temp to my system, and start pumping some hot water? I need 120 to 130 minimum, as that's what my system is designed for.

I sincerely doubt that...

A: ...your system was ever actually "designed"...

...or...

B: ...that it it "needs" 120F-130F entering water temperature for the radiation to make it work.

You can get a bigger delta-T out of the boiler by slowing the flow on the primary loop, but you need to be mindful of the minimum flow requirements and the maximum delta-T (which I haven't looked up for the ECO 110, but you should.). You can get a bigger delta-T out of the radiation by lowering it's flow rate too.

But let's start with the absolute raw basics. Has anybody done a full Manual-J type heat load calculation for this house? If yes, what is the 99% design heat load, and how many square feet of active slab radiant is there?

Is the slab insulated at either the edge or sub-slab? If yes, is it edge-only, sub-slab only, or both( and at what R-values)?

 

[Sponsor]

 

[Dana]

BTW: As currently configured, how long are the burn times (to the nearest 5 seconds), and how long is the off interval between burns?

What kind of delta-T are you seeing in to out on the boiler itself (not the radiation)?

According to Figure 41, p47 of the manual, the minimum flow rate through the boiler is 5 gpm, the max is 10gpm. According to Figure 43, p,38 pumping head is 0.3' @ 5 gpm, 1.2' @ 10 gpm, so the primary pump has to be pretty tiny to NOT over-pump to an even lower delta-T. The minimum fire output of the -110 is ~21,000 BTU/hr, so at the max legitimate pumping rate of 1o gpm (~5000lbs/hr) the delta-T would be a very low 21,000 BTU/5000 lbs= 4.2F. At the minimum legal flow rate of 5 gpm it would be twice that, or 8.4 F.

At the max firing rate output of 100,000 BTU/hr it would be delivering a delta-T of 100,000BTU/5000lbs= 20F at 10 gpm, or 40F at 5 gpm.

In Figure 48, p.44 the recommend some pump and speed setting recommendations at different delta-Ts & pumping heads. Unless you've run the numbers on the pumping head of your boiler loop it's hard to say how relevant any of those numbers, are, but for the record, what pump is installed, and what pumping speed (if multi-speed)?