Bradford White Combi gone bad? Options?

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Platinum_Overcast

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Hello all-

I've got a 2002 (according to the SN) Bradford White Combination water heater. It's a 75 Gal, 76K BTU input natural gas water heater with an integrated heat exchanger that feeds a radiant in floor heating system. Model number is M2C75T10EN12.

Problem:
I believe that the heat exchanger coil has developed a leak and the DHW is now combined with the radiant heating loop. This seems to be somewhat common on these systems from that era according to a bit of googling. I'm assuming one of the pros here has seen this before?

How I got there:
I decided to check on the expansion tank and see what the air pressure was. First time since buying the house in 2009. Pressure was zero. Pretty sure that's not right. Turned off the main, opened a hot water tap at the utility sink and tried to pressurize the tank with a bike pump to something like 12 psi or so. Wouldn't take any pressure, like the Schrader valve was bad. Poked at the valve, the needle moves fine. OK, assume the expansion tank is dead....

Looked at the pressure on the gauge for the radiant zone, read 8psi. Maybe a little low, but made sense to me...

Closed the tap on the utility sink, opened the main and noticed the pressure gauge on the radiant system swing all the around off the scale on the top side... 60+ psi. Hmm. That doesn't seem right.

Static city water pressure here is 63 psi (I measured it when we built the irrigation system in 2014).

We've also noticed at least one of the hot water taps puts out a bit of discolored water on the first use of the day. It's been doing this for several months at least. Red (rust colored, actually) herring perhaps? Indicative of the tank itself gone bad?

So...

Question 1: Am I right that the heat exchanger coil has been breached in the WH? Or have I missed something?

Question 2: If so, this is obviously bad. Nothing will kill us in the next couple weeks, right? I've read about legionella, etc. but this has probably been happening for quite awhile without our knowledge. It's winter here in Minneapolis and the radiant system is circulating, we're using hot water, etc. Everything is working "fine".

Just want to confirm that I'm thinking along the right lines and it really has gone bad before we start talking about options to replace it. I've been doing quite a bit of reading here and elsewhere and I feel like a plan is coming together, but I'd really appreciate input from the forum on what I'm thinking.

Thanks in advance!
 

Dana

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What means "Closed the tap on the utility sink, opened the main ..."?? What is "the main"? If you opened a manual fill valve to the system it SHOULD go to the full potable water pressure, and the system would then need to be bled down to a more normal pressure.

Most heating systems will have a full drain valves somewhere with a standard hose thread. Temporarily installing a pressure gauge on that tap and opening the valve would tell you if the system is pressurized to the full city pressure and would be a sanity verification on your system pressure gauge. (Re-measure the city water pressure at a hose tap using the same pressure gauge. If you install a hose on the system drain and open the valve to bleed down the system to a reasonable pressure, then give it a day- or two. If the pressure keeps rising you have a leak.

If the system has an auto-fill valve designed to keep the heating system water from running dry, it could be the auto-fill valve that is leaking, not the heat exchanger.

It's a bit unlikely that system water would be leaking into the potable side- the more likely scenario is that a leak just overpressurizes the heating system. Rusty hot water could either be stuff that came in from the city, or the liner of the tank has begun to fail. This is probably a glass lined tank, and only good for a dozen years on average. If it's 14 years old and still going you've perhaps beaten the average.

If the expansion tank is bad it'll thud rather than ring when you rap on it at the air-valve end- it's full of water. If it's bad, replace it, checking the pre-charge before pressurizing the system.
 

Platinum_Overcast

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What means "Closed the tap on the utility sink, opened the main ..."?? What is "the main"? If you opened a manual fill valve to the system it SHOULD go to the full potable water pressure, and the system would then need to be bled down to a more normal pressure.

Thanks Dana. Sorry for the confusion - I meant when I turned on/off the main shutoff for the whole house. I haven't touched any other valves, and I need to check if there is an automatic fill or not. That's a great point about an automatic one failing (if it exists).

The expansion tank thuds (same sound on the air and water side) and sounds much lower than the new replacement I have sitting on the bench (bought it when I thought that was my only problem).

Pressure checking at the drain and then draining to a lower pressure to see if it creeps back up makes sense to me. I'll try that next to confirm.
 

Platinum_Overcast

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After further investigation:

No automatic fill valve in sight.

Static pressure measured at the drain valve (return side of the radiant coil where it enters the WH) is ~68psi (city pressure).

I think that means there's a leak that's pressurizing the radiant zone.

Side question #1: Where I measured the pressure is the only boiler valve I see in the radiant zone. How did they purge the system in the first place? Through the air eliminator only? Am I missing something?

Side question #2: If the glass lined tank of this unit is failing right on schedule... why do people people pay the premium to install one of these Combis if its lifespan is no different than the basic WH? Wouldn't it have been smarter to delegate the heating duty off to something with a much longer lifespan?
 

BadgerBoilerMN

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This is a common problem.

Here in the Minneapolis Metro there are thousands of multi-level homes, mostly suburbs, with the Bradford White Combi-Cor water heaters (both 50 and 75 gallon models, power vent and gravity/naturally aspirated), heating both DHW and living space--usually found in walk-out basement.

The reason for the success of the the BW Combi water heater is the small footprint, same as a conventional tank, and the ability to heat space with the incomparable comfort of an, already specified, basement slab. Though the concept was good and obviously widely accepted, the execution, both in terms of manufacturing and installation were spotty.

In our market the Combi failed--most leaking heat exchangers covered under a generous 10 year warranty--at an alarming rate. The company, to their credit, stood by this material "tank" warranty but did not cover labor--the industry standard. It did not help that Minnesota required the use of a heat exchanger, which correctly separates heat transfer fluid from potable water, but over-engineered this reasonable and affordable safety factor by requiring the fuel-wasting and leak-producing double-wall heat exchanger.

But a near-monopoly market for more than 10 years backfired.

Still the company has introduced several "improvements" to the original design including new anodes that have plugged up the plumbing of more than one of my customer's plumbing systems.

Now that Minnesota has accepted the UPC we can ditch the double-wall mandate, if not the Combi altogether, and use a dozen different combi water heaters and boilers on the market today. We typically offer three alternatives including an atmospheric tank water heater much like the combi, sans the internal heat exchanger and efficiency upgrades including the A.O. Smith Vertex and HTP VersaHydro.

Some will go with a direct replacement and accept the double-wall--still all they have in stock--but many, especially those who have suffered one or more replacements in the past go for our upgrades. You can probably get on installed Monday morning.

The most likely reason that your system still operates is that the installer forgot to install a proper pressure relief valve on the radiant or "low side" of your combi system. Ironic that the most rabid plumbing inspectors in the Cities would insist, up until a few weeks ago when the new code took effect, that certificate be producing "proving" that the combi space and water was manufactured with double-wall protection, but entirely missed the most important and foolproof safety feature assuring the control of potentially dangerous over-pressure and cross-connection...the lowly 30# safety pressure relief valve.

By the way, you will need a new expansion tank on the heating side, among other things.
 

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Thanks for the insight Badger. I kinda assumed this was the case and have been doing some research to try and figure out the best options to replace it. There's been some really outstanding posts from you and others here that have hopefully informed my though process.

Some details about the house:

  • Minneapolis, MN
  • 1930 construction, 2 story
  • Newer windows and doors everywhere (MAC noise remediation circa 2000)
  • About 2000sf of finished space (1st and 2nd floors)
  • Basement
    • 1000sf
    • Unconditioned and unfinished
    • Home of the boiler and WH
  • First Floor
    • 1000sf
    • Cast iron radiators
    • 76K BTU input, 63K DOE conventional boiler from ~2002. Atmospheric vent. 80% efficient. Controlled by a thermostat on the first floor.
  • Second Floor
    • 1000sf
    • Extensive remodel in ~2002
    • Radiant in floor
    • Fed by the bad BW Combi. Atmospheric vent, controlled by a second thermostat on the second floor.
The way I see it, I think there are three options with a couple variations.
  1. Replace the BW Combi directly with a new unit.
  2. Assuming the conventional boiler has enough capacity - rework it to run both floors. Buy a new conventional or tankless WH for DHW only. Both units live next to each other in the unfinished basement. Lots of room to reconfigure relatively easily.
  3. Buy a new mod con boiler with indirect DHW and have it do everything. Perhaps the increased efficiency makes this somewhat worthwhile.
With that in mind I started figuring the demand for the overall system. I've come at it a few different ways and seem to get numbers that are all in pretty good alignment.

Approach #1: Manual J

I worked through the coolcalc.com web app using a couple different models. Made a first pass by simply taking the three floors and ballpark measurements. Went back and did it on a room by room basis with real measurements. It's giving me a total demand of 55K based on a 70F indoor and a -11F 99% day. That's pretty well in line with the 25BTU/sf rule of thumb. I can post the report if that's helpful. Hopefully there isn't a gross error in my assumptions.

We actually run the house at 68F on the 1st floor (setback to 60-62F at night) and a constant 64F upstairs in the bedroom with the in floor system. Open stair between them so I'm sure the convection skews things plenty.

Approach #2: HDD, 99% and actual usage.

I pulled the HDD on a daily basis from degreedays.net and broke it out to align with the billing cycles and natural gas report from CenterPoint for the past 2 winters. I got rid of the summer and shoulder seasons and only used the data from the full on winter seasons when both the first and second floor systems are operating. The thread here is what I based the approach on: https://terrylove.com/forums/index....based-on-therms-hdd-and-99.60554/#post-449886 Interestingly enough, they have a pretty similar situation here in the Twin Cities and come up with similar numbers.

Playing around with a few different reasonable base temperatures gives me something near 40K BTU for our house. Again, seems pretty reasonable. From what I understand a Manual J calculation has some conservative factors built in.

Approach #3: Boiler runtime according to the Nest thermostat and radiator capacity

The Nest controls only the first floor radiators running off the conventional boiler. In mid January we had a cold snap that was pretty close to the 99% day. We happened to be on vacation at the time, and set the Nest to 60F on the first floor (still 64F on the second floor on the other thermostat). With no activity in the house the Nest reported a total runtime of about 9-10hrs per day. Very regular cycling to maintain that temperature - probably 20+ cycles. Maybe not the best thing for the boiler, but it did give a unique test case.

10 hours at 63K BTU/hr /24 hrs = 26.25 BTU/hr Avg

Next, counting/measuring up the radiators and using the numbers here: http://www.expressradiant.ca/pdfs/product_classic_sizing_how_to.pdf

I get a 1st floor radiator capacity of about 24K BTU at our 130F conventional boiler operating temperature. Since this reperensts only about half the square footage, seems like the right ball park once again.

So with all this mind, seems like the conventional boiler has enough capacity to take over duties for both floors? Obviously there's some plumbing, circulation and controls to be worked out. I'm sure the chemistry in the original CI radiator system is also pretty unpleasant.

Going back to the original options, I think all three are in play. I'd appreciate feedback on my thought process so far.

Badger- I know you do this for a living here locally and have probably seen very similar situations. Any rule of thumb for how the costs and savings play out? I know every situation is unique and there's no substitute for a real assessment and quote. I'll probably be reaching out for one of those shortly either way.

Also, I've seen a couple posts on the Viessmann 222-F. Seems like it might be tailor made to replace both units in our situation. Any chance the rough ballpark numbers work out to make that a real option? I'm sure replacing a fully working but less efficient system would never pay off, but given that we have to deal with the failed Combi one way or another, perhaps it makes sense?

Thanks all.
 
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BadgerBoilerMN

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From the last to first.

I really like the 222F but, like so many combi-boilers it is really tough to match a boiler with that reasonably matches the heat load and the DHW load in an on-demand fashion. The addition of DHW storage makes is somewhat easier but as it relates to your modest space heating load, the minimum fire would be too much nearly all the time. Had you both floors still full of cast iron rads I might entertain it. Still only Manual 'J', and maybe Dana, knows for sure.

You know I am nearly irrational about the many merits of ModCon boilers and combining them with indirect water heaters makes them irresistible but, you have a relatively new boiler with an expected lifespan of 30 years...

I hate waste. So if you have a good chimney I would look to a mixing strategy dependent on a per-floor heat load that would determine the design water temperatures for each. Depending on the type of radiant floors installed you may get away with a single design temperature. Mixing to protect an atmospheric boiler can be expensive, especially if you would like to include ODR.

In any case a nice single-wall SS indirect water heater would give you about 30 years service and make you ready to shut down that nasty chimney the minute the old boiler pees on the floor.

I would have never used a Combi for your application. Many are confused, no less the "professional" about the proper application of certain gas-fired appliances. So many to choose from, it spins the head!
 

Dana

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A fuel use against heating degree-day calculation would be a more accurate means of nailing the actual heat load than most online load calculators, but it's an upper bound. Only mid or late winter meter readings should be used. In the spring/fall shoulder seasons hot water use and solar gain can skew the numbers considerably. Your real load is likely to come in a bit under 40K, unless your basement is NOT insulated. (If the basement isn't air sealed and insulated it's definitely "worth it", even if you're never intending to convert that to living space. Losses from an uninsulated basement is usually 15-25% of the total heating fuel use.)

I'm with Morgan on this one- run the radiant off the existing cast iron boiler, which is still something like 1.5-2x oversized for the whole house load, and install an indirect operated as a priority zone. The current load on the cast iron boiler can't be more than about 25K, but it could be as lowa as 20K. With 63K of output there's no way it's as-used AFUE going to hit it's 83% steady state efficiency since even on design day it would not be running more than about a 35% duty cycle for heating the actual zone. The 42% duty cycle reported by the NEST is higher than 35% since it's spending part of that run time ramping the boiler back up from it's cooled-down idling temperature. By giving it more load and a higher duty cycle it's as-used AFUE will approach it's labeled AFUE (pretty close to it's steady-state efficiency numbers.)

When the cast iron beast's time is up you'll have a better idea as to what to replace it with. Since it's only middle-aged at ~14 years of service you're likely to have a decade or more to contemplate it unless it's being abused. If you're running the boiler's OUTPUT at 130F you could be damaging the boiler with condensation on the heat exchanger plates. Even if the radiation keeps up at an AWT of 130F or less, the entering water temp at the boiler really needs to be higher than 125F. Setting a higher boiler temp with a bypass branch in the near-boiler plumbing to keep the EWT high enough at the boiler allows you to run the radiation at a lower temp without risking the boiler.
 

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Morgan and Dana -

Thanks for the thoughtful analysis. It makes a lot of sense to me.

Basement is uninsulated and very chilly down there.

As you say, we have no desire to make it into livable space but I can see where the insulation could make a huge difference. If we're doing that, then it probably makes sense to finish the exterior walls. Maybe rework the laundry area... and the workbench... the plumbing gets tidied up by the boiler... maybe tuck some into the rafters at the same time... a warm floor would certainly be nice... and then maybe... and so it goes. :)

Another wildcard is a potential plan to rework the back entry mudroom into conditioned space to open up the kitchen area a bit. I can tweak the Manual J calc to get a difference for the planned space based on the excellent response Dana provided in the thread I linked above. I'm guessing there won't be enough excess radiation capacity off the kitchen radiator as it stands, perhaps it will make sense to extend the zone with a panel radiator.

Surely we are into the realm of every situation is different and will need some professional insight into options. Just getting some of our ducks in a row before we give you a call, Morgan. :)

I'll clean up my HDD spreadsheet a bit and post it for those that might want to use this method in the future.
 

Dana

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Current IRC code min for basement wall insulation would be the performance equivalent of R15 continuous insulation. Minnesota's building code prescriptives for basement insulation starts with a requirement for a minimum of the R10 of the total being on the exterior side of the foundation wall. Most building inspectors would give you a variance on that in a retrofit situation, but make sure anything you do that's not compliant with current code gets approved ahead of time.

I did my basement with 3" of reclaimed rigid roofing polyiso held against the wall with 1x furring on which the gypsum board is hung (a requirement for fire code with foam insulation), which comes in at about R16-R17 after derating the polyiso from it's labeled performance to better reflect it's performance at lower average temp. A comparable-performance assembly that works in MN would be to install 1.5" of foil faced polyiso or 2" of EPS trapped to the foundation wall with a 2x4 batt-insulated wall, with no interior side vapor barriers. Sealing & insulating the band joist and foundation sill with an inch or two of closed cell foam would also be in order, or cut'n'cobbled rigid foam sealed in place with can-foam. If going with a studwall + foam approach don't cut corners on the foam- you need at least R7.5 in your climate for wintertime dew point control on the above grade section or it will collect moisture in the batts at the cold edges of the studs, increasing the mold risk.

A third, quicker but more expensive solution is to do it all with a 2" shot of 2lb density closed cell spray polyurethane painted with intumescent paint for fire safety. That's only R12-R13-ish instead of R15, but it's nowhere near cost effective to go any more than that with spray polyurethane (about $2-2.50 per square foot.) The HFC245fa blowing agent used for most 2lb polyurethane is also a very powerful greenhouse gas ( about 1000x CO2), but there are a few vendors using lower impact goods now. Lapolla uses an HFO1234_ _ variant blowing agent, and Demilec just announced they will soon be phasing over to an HFO blowing agent from HFC245fa (stay tuned.)
 
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