Not enough hot water--need help!

That shows the importance of paying attention in English class!—NBC

I also see that the circ may be slightly undersized. Not enough to really jump at but the tank requires 14 gpm and the coil has a pressure drop of 6.2'
That land right on the performance curve of the 0015 set on hi. However, that does not take into account the extra pressure drop of the associated piping from the boiler to the tank. It also doesnt account for the extra pressure drop of 1" pipe rather than 1-1/4".
So with that being said, you are looking at a 0010 or a 0012

Dave H.

The way I learned it is based upon the BTU capacity of 1 gal of water which is rounded off to 10,000 BTU's. 10,000 BTU's into 140K=14 gpm. Is this the right concept?

There is no check valve in the picture. Some of those circulators have an internal one in the throat. Usually there will be a sticker on the motor indicating it is.

Do you have the specs on the old HWH? Usually those are < 40k btu

The water does not care about arrows on the pumps or where you want it to go. If you don't have check valves on both circs, the water will flow backwards through one circ when you are trying to satisfy the load on the other. On occasion the mixing valve can backflow as well.

What area are you in. Your system should be performing better that the old system. Maybe a fresh set of eyes would help.

I can't see from your photos where the supply from the boiler to the tank takes off. Is it after the B&G IAS on the manifold after the zone valves?

Zman is right, water moves from high pressure to low pressure and you have to have check valves to direct the flow where you have bifurcated runs. That means a check valve for the black pump and one for the green pump. If the green pump is a newer pump, the output of the volute probably is channeled for a plastic check valve if it doesn't already have one. If it has one, the installer should have put a IFC (Internal Flow Check) sticker on the back of the pump. Your pump is a Taco 0015 MSF-IFC so it should have a IFC. Caleffi make an inline flow check with a high CV (low flow resistance) that can be mounted vertically or horizontally and that can added before the black pump. If you have indirect tank priority over space heating, I would expect that the Honeywell zone valves would stop the dynamic flow but without a check valve on the black pump allow thermo-syphoning to the heat emitters on the upper floors, but that may not be a big deal.

BOTTOM LINE--You ain't got the flow, babe. You have a Taco 0015 MSF-IFC pump, did anyone look at the pump curve for speed 3? At 14 gpm it has 6' hd. Damn, your HX has 6.2' hd + boiler and piping pressure losses. When you don't have the heat I always think of flow, first. Flow is the conveyor belt that transfers heat energy. Measuring the temperature differential between the boiler supply and the return at the HX would have told you that. It would have been a wide differential.

Kunisk, you have a convoluted piping arrangement, it could have been done a lot better and if you had chosen a tank with boiler ports on the side rather than on the top, you could have shortened your pipe runs by 2/3.

You are going to figure out your pressure losses on the indirect circuit and choose a pump that would give you 14 gpm at that head loss.

I haven't seen a pressure loss vs flow chart on that tank HX, but at 11gpm you have 9' hd with that pump. The HX pressure loss would drop to maybe 5' hd which leaves 4' hd for all the other pressure losses in the system. I think with that pump and sys losses you have a lot less flow than 11 gpm.

if the boiler is cycling on temp while doing the DHW, then there is enough boiler.
The flow isn't getting to the domestic tank.
The heating circ, or both circs, need backflow(s), to direct the boiler heat to the domestic tank.

Kunisk, you can take 'hot rod's' advice and put in low flow shower heads or put restrictors in the existing shower heads. By the way, what is your domestic water pressure? You could lower that if it is too high.

@SemourCates

Your DT of 20 occurs when the tank is full of hot water at 160 degrees. No one is complaining when the tank is full of hot water. We are concerned why the boiler is reportedly cycling when the tank is hypothetically luke-warm.

looking back at your early pictures,
I do see zone valves on the heating circ loop,
are those zone valves closing when you get your domestic heating priority?
or is the "scorching hot" domestic heating water flowing back thru that heating zone and not direct to the boiler?

at the domestic tank,
is the "scorching hot" even in and out? can you feel or measure a difference in the heating supply and return at the tank?
(got 2 more strips of that temp tape?)

When the dhw has finished cycling, feel the piping on the inlet side of the dhw pump for temperature changes when the heating cycle begins. If you sense a change of temperature, there's no check valve in the pump. Same for the heating circuit.
As was mentioned already, both circuits need check valves.
Suppose the installer didn't add a check valve to the heating circuit. Cross flow between heating and dhw may be responsible for lack of flow in the boiler and indirect tank resulting in the short cycling and slow recovery.

Our 38 gallon indirect makes hot water faster than we can use it. I found out quickly when I installed it that my heating circulator had no flow check. 160 degree water in the cast iron rads was a good clue when 130 is the max on the heating cycle. I added a flow check to the heating circulator and the two circuits work exactly as they should.