Crown XBF-150EID LP Boiler Questions

[amkazen]

Hi,


I am looking for some guidance on my 15-year old Crown XBF-150EID LP boiler. Should we replace the gas valve only, the gas valve & aquastat, or just live with the two items right now, not replacing them, and replace the boiler before the Fall with a wall-hung high-efficiency unit? What would you do? We have a phenomenal plumber now and trust him 100% but I always like to have some sort of comprehension on a subject before making a decision, and right now I am confused.


Here is a list of the components in this combination radiant in-floor and domestic hot water system, installed in Spring of 2002.

Crown XBF-150EID LP boiler

Honeywell Aquastat Relay type L8148E

Honeywell VR8204A 2241 gas valve

TriangleTube 60-gallon indirect hot water tank - installed January 2016 - 1 year ago


Issue: In early December 2016, boiler did not heat water and I discovered soot had fallen around pilot light area, probably blocking the pilot from igniting. As soon as I cleaned the igniter, the pilot came on and we had hot water soon thereafter. This has happened about 4 times since, and even when it has not, the area under the igniter is often covered with soot.


Resolution: 2 days ago the plumber was out and took the sides completely off the boiler and cleaned everything. He said the burner tubes were clogged with dust and lint, a mouse was living in there (not sure where in a boiler it could live), and that the gas pressure was half of what it should be. The next day his troubleshooting told him the propane regulator is ok but that the boiler gas valve is not allowing enough pressure to meet manufacturer specs, and recommends replacing it.


Compounding factor: Plumber states floor heat requires 120*, water heater needs 160*, and boilers lowest temperature setting is 180*, and that equates to a lot of gas being wasted. This is the system that was installed in 2002 when the house was built and was what I was told was needed. He states the choices are: going to a wall-mounted IBC boiler before next fall, or changing the gas valve and aquastat (now also the aquastat, vs. just the gas valve?) He also states we can get by with it as is as it has been running this way since new, just very inefficient.


Confusion:

1) 1st, the gas valve needs to be replaced, but now it looks like the gas valve and the aquastat both should be replaced simultaneously. Can only the gas valve be replaced or is it better practice to always replace both at the same time?

2) Since it is running inefficiently from installation in 2002, and since the temps above indicate the boiler heats the water higher than what the floor and water tank require, I immediately jump to the conclusion I was sold the wrong system in 2002

a. Plumbers reply is that Crown boilers are a quality product and that it is the installer’s responsibility to adjust temp and gas pressure upon installation

b. He also stated he did not know if gas valve went bad or was set-up incorrectly

3) I am confused in that is the gas valve adjustable? Hmmmmm…..I just read the gas valve might need to be converted from natural gas to LP by the use of a flange….I wonder if the gas valve is not set-up for LP and is why the gas pressure is low…for 15 years? Would it even work ? Well, it has but still…..


Looking on-line I see the gas valve ranges from $109 to $150 (Robert Shaw 720-079) to $233 (WRD 36H32-304). The aquastat ranges from $170 - $300. I am guessing the cost replace these two items would be $400 in parts plus labor and I am unsure how many hours of labor....4 hours, to include adjusting, setting, etc? So, using $80 per hour as a rate that would be $320 plus $400 plus tax so I am looking at $800 or so, vs. living with it and replacing the boiler before next Fall.


What are your thoughts?

 

[Dana]

Excessive soot is an indication of an improper fuel/air mix. If you are at a high altitude ( higher than 2000', which is most of NM) you may need to make adjustments to get the proper fuel/firing rate to get the proper fuel/air ratio, which could be attributable to the gas valve. Replacing the gas valve is more than just an efficiency issue: With an overly-rich mixture the carbon monoxide levels of the exhaust are several orders of magnitude higher than they should be. If the aquastat is mis-calibrated but k

Even with derating for altitude the Crown XBF-150EID is a heluva lot of boiler for most houses- it most likely IS the wrong boiler for the house.

The lowest high-limit setting could be as high as 180F (but it's probably lower) and it's low limit should be MUCH lower. That is not a lot of fuel wasted, though it does raise the temperature of the boiler room. If the boiler room is insulted from the outdoors, the vast majority of that heat stays in the house. Lowering the high limit to 160F would save at most a couple percent. But insulating all of that manifold plumbing with 1" wall thickness fiberglass pipe insulation (as it should be, especially if the boiler room isn't insulated) would cut the standby & distributions losses by a similar amount.

Bottom line: Replace the gas regulator, keep the aquatstat, then take your time on the new-boiler decision. Don't just take the plumber's word on what you need.

Before plunking down any cash on a new IBC or other new boiler, run a heat load calculation. Since you have a heating history on this house, an easy and accurate way to establish an upper bound on the design heat load is a linear approximation using propane use against heating degree-day weather data from a nearby weather station. Sounds complicated, but it's really 5 th grade arithimetic, and gathering propane fill up dates & quantities, and looking up the heating degree day data. The details of how to make that calculation lives here. If you're willing to share your ZIP code (for 99% outside design temperature and weather data purposes) , some wintertime propane fill-up quantities and exact dates I can walk through that calculation here.

Since the new boiler will be a modulating condensing type, it's very important to understand the limitations of your existing heat emitters and zoning set up to know whether it's going to short-cycle itself into an early grave on zone calls. Looks like you have a total of six zones (?). (Short cycling the ridiculously oversized Crown boiler on zone calls may be contributing to the soot and efficiency problems too.) The napkin-math analysis on that lives here.

If you were to replace the aquastat, replace it with a heat-purging economizer control, (eg Intellicon 3250 HW+ ) not just another dumb electromechanical type. This will limit the amount of short cycling on zone calls and the amount of distribution & standby losses by "learning" the system based on it's behavior, anticipating the end of a call for heat from a zone early, and purging heat from the boiler to finish the call. On a new call for heat it will purge heat from the boiler into the zone radiation until it hits the low limit (whatever you program it to- 135F is fine for most propane boilers, but it need not be higher than 140F no matter what) then letting it go to the boiler's maximum high limit. That results in the longest possible burns, and the fewest number of burns, both of which are important for efficiency.

If I had to guess, in a 6 zone system with a boiler that's likely to be 3x oversized for the whole-house load (typical), the boiler is more than 10x oversized for any individual zone, and the average burn cycle length will be under 200 seconds, which is an efficiency-emergency for a cast iron boiler.

 

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[Jacobsond]

I would find a boiler/furnace repair guy and ditch the plumber. Your description sounds like he is guessing. Need someone that can preform the required maintenance and do a combustion analysis if your getting sooting on a propane appliance.

 

[Jadnashua]

If it was a burner setup from the factory as NG, and you ran propane through it, it would use huge amounts more gas than it should. It's not just the regulator that is different between NG and propane, it's the jetting, where NG needs a bigger jet to have the same capacity as the higher energy density propane fuel.