Troubleshooting crossover with boiler system

Brand new custom home with new lochinvar 80 gallon boiler specked for my size home. Trying to troubleshoot not enough hot water by doing some tests to see if there is a crossover issue. I'll skip everything the plumber has tried so far for now. One thing he still just won't take the time to do is test for a crossover problem, so I took it upon my self to try and I'm not sure if my findings mean anything.

I turned off the hot water main line so it won't flow into the house. Turned off the recirculation valves and pump. I opened up hot water faucets from basement to top until no more water came out. Now to my observation that I'm not sure if it is weird or not. I tested the cold faucets. Kitchen/sink etc all run the cold while no hot. BUT, 3 tubs out of 2 ran super cold water, the other 2 a trickle of warm water (but it could be warm from sitting in the pipes). The master shower (two sided controls) both ran cold. One of the tubs that ran cold water has a stand alone shower right next to it and would not run cold water, just a trickle and it was warm.

Are these all determined by the cartridge valves? As in, would some prevent the cold water from coming out? Again, the cold water doesn't come out of these if I turn off the hot water to the house.

Also, the home is on a recirculation system, so I don't know if it's an issue that sink faucets start room temperature, almost warm and 20 seconds until ice cold. And the toilet tanks fill the tank with warm water in basement and main floor bathroom (closest to boiler).

Any input would be greatly appreciated, I'm about to pull my hair out. Plumber wants to replace the cartridge valves in master tub and a sink in the master but I don't think that will fix it. And he just won't take the time to test for any crossover issues.

Thanks!

Shortened question to my problem. If the hot water supply is completely turned off and all hot water from pipes relieved, should I still get cold water to come out of all fixtures including bath and shower? 1/2 do and another 1/2 does not when I do this.

Just for starters to see if a crossover exists, do not use any single handled faucets (sinks or tubs or showers). Find a fixture that has a single hot on the left and a single cold on the right. Preferably on a higher floor, the higher the better.
Shut off the valve to the hot water tank.
Open the hot side of the fixture faucet only. No other faucets or fixtures should be running.
If you get cold water out of the hot side open fixture, you have a crossover.
Check your recirculation line for a properly installed check valve.
Out of curiosity, if this is a brand new custom home, how long has this problem existed? How old is the home?

Thanks for the response, I will try that.

We've been in the home for 6 months is all. Brand new 80 gallon, 110,000 btu/hr input. Was told we could run a LOT of hot water. First signs were problems after master tub (it's big) was filled, you couldn't even use the pull shower head after. Filled with a person is about 45 to 50 gallons. Plumber came and I believe he added more piping by the boiler and the tank. I believed he added a new mixing valve (no plumbing experience) and CRANKED up the heat on the boiler. Inlet and outlet temp always around 172-176. Mixing valve has a control to throttle down to 115. Circulation therm shows 102-105.

That helped a bit...you could use the pull shower head. Lucky to get more than five minutes shower somewhere else (basic shower). With school, we just figured maybe the family was all using water at the same time at night (bed time). But just the other day, I put my son in his shower and it was barely warm. Found out that my wife took a bath (no hair rinsing) a full hour before and that was it.

My concern is that the plumber didn't "fix" the problem. He's just pushing the limits to my boiler. He's blaming possible crappy cartridge valves maybe in the master tub or a master bathroom sink. The bathroom sink did low water pressure and warm water coming out of the cold, but it ended up being a kinked hose. He still told me to order new control valves for them.

In the beginning he also tried to blame water use by how many gallons we used a month. Not being a plumber, I still knew to ask if it is more about the gallons per minute we're using. He didn't want to go down that path. To humor him I still called the city and they told us we were using 50% less water a month than average.

So I'm trying to figure out if it's a plumbing issue or a boiler issue. Everything I've heard about my boiler is that it's a really good one. Plumber just want's to blame the different brand plumbing fixtures we had installed outside of his agent.

Side Note; If you just had this custom home built approx. 6 months ago and you are having these issues, be sure to document EVERYTHING said and done by you and the contractor(s) or builder. Too many times we have heard on the forum, and seen in real life, under qualified and unlicensed contractors screwing customers out of the quality promised during the sale.
IMO, there is no reason to have your water heater temperature turned up so high. Even with a tempering valve, most codes strictly prohibit temperatures above 140 deg. F. The failure of a tempering valve could cause immediate scalding and severe burns even if they are supposed to be fail-safe.
It may also help, after you do the preliminary testing described above, to take some pictures of the piping around the water heater, recirculation connection (pump, check valve, etc.), mixing valve and whatever other stuff comes to mind that may seem to be relevant and maybe something will jump out at us.
Last, for now, who supplied and installed the fixtures? I can't figure why you would be bothered with ordering any parts for fixing a problem that somebody else should be responsible for on a newly built home.

Had a friend who own's an industrial HVAC company with plumbers give me a theory. He says I have no real Boiler Loop in place. The circulation is way too short.

He checked the specs of the system and yeah, I should have enough to keep hot water in my house and my neighbors. He says that I don't have a big enough boiler loop. I look at the piping and the loop from the boiler to the tank is very short. The plumber tried to compensate by adding a mixing valve and cranking the cycle temperature to 172 which is going to shorten the life of my boiler. When you draw the master bath, the temperatures plummet really fast. I was told that if the loop was as big as it was supposed to be, or if I add a tank, the circulating water would be warm, almost hot and a much greater quantity of it to circulate. Enough to keep the cycle going strong. Instead, my loop is short and the compensating water is the cold water inlet. With winter weather, I can see why this is a problem.

So is that a common term and could it be a solution? Boiler loop?

The build was a nightmare, although the house turned out beautiful. Unique situation too long to type the whole story out. 1st contractor fired and sued after caught stealing money and grossly underbidding the house. 2nd contractor was licensed and a personal friend who lowered the contractor fee in 1/2.

Thanks!