Mod-Con Combis with full documentation and controls for DIY
I am looking to replace three HTP Munchkin T-50s installed with indirects for DHW. I am focusing on combi units for space-saving reasons. I have maintained these for the past 20 years myself, including annual maintenance as well as diagnosing issues and repairs, including control board, blower motor, wiring harness repairs/replacements. I have been looking at Navien, Rinnai and HTP (although my Munchkins did have more than what I would consider their fair share of quality control (wiring harness) issues).
My question is, from set-up to maintenance to diagnosis (error codes, etc.), which companies provide the best documentation to DIY folks like me. Of secondary importance, are any better or worse in terms of ease of servicing?
Thank you.
Comments
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In my opinion, Lochinvar Noble boilers cannot be beat in either of those areas- everything is plainly displayed in English rather than codes, and they have a significant amount of space inside (and side panels can be easily removed if necessary). They have both wall and floor units in combi form. With that said, the end users of the domestic water are probably not going to be thrilled with a combi after being used to an indirect but maybe you don't care. I've tried a few of everything and the Noble is a real workhorse, I have several hundred of them in service and can count the callbacks on 1 hand.
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I am in the same boat and have found that Burnham / US Boiler have excellent documentation and after-sale technical support. Download one of their manuals from the website and take a look. They even include internal wiring diagrams and full parts reference. I am replacing an old Burnham MinuteMan with a Burnham Alta for this exact reason. The only gotcha is that Burnham seem to be (relatively) new to the “mod con” market.
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Combis are usually the worst option. They need to be drastically oversized for the space heating load in order to make hot water on demand. This leads to increased cycling and higher costs of maintenance and repair. I would never recommend installing one especially if you have room for an indirect.
The brand of the boiler doesn't matter as much as the quality of the installation. Who is doing the job is more important than what brand is being installed, however I would recommend staying away from Navien.
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I think you may be unpleasantly surprised when you go to set up the Alta. The control is possibly the worst design of any mod/con boiler ever built. Great boiler, but the control is beyond terrible.
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Do you have gas training and a combustion analyzer? That’s required on most every mod/con.
I agree about combi’s - most of the time, they’re a terrible choice. Go with a heating boiler and an indirect.
Another thing to consider is that most manufacturers will not give technical support to homeowners and DIYers. And most warranties will not cover equipment that is not professionally installed by a licensed contractor.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
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SuperTechMember Posts:2,2151:55AMCombis are usually the worst option. They need to be drastically oversized for the space heating load in order to make hot water on demand. This leads to increased cycling and higher costs of maintenance and repair. I would never recommend installing one especially if you have room for an indirect.The brand of the boiler doesn't matter as much as the quality of the installation. Who is doing the job is more important than what brand is being installed, however I would recommend staying away from Navien.Thank you for this. I am curious, you even see short-cycling with 10:1 turn-down ratios? Space is indeed at a premium, which is the reason I am considering combis.
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You can indeed get serious short-cycling, even with a 10:1 turndown. This is particularly true if you have smaller zones. Suppose you have a nice combi running around 200,000 BTUh at full song, so as to accommodate your hot water needs. And suppose you have a zone on a moderate day which requires 5,000 BTUh to stay warm. That boiler is going to short cycle.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1 -
Yes I definitely see them cycling excessively,even with the typical 10:1 turndown ratio. Just the fact that the boiler needs to make hot water on demand leads to excessive cycling. Combis are typically very high maintenance and I find they need repair more often than anything else. Also the fact that many parts are model specific is another problem. An indirect tank is simple, easy to repair and will usually outlast any combi with little maintenance required.
Almost all condensing boilers and combis need to be setup and commissioned by someone who is trained on combustion analysis and equipped with a digital combustion analyzer. Almost every combi and condensing boiler that I see fail prematurely is a result of improper installation and commissioning. If you insist on a DIY install please follow the manual closely and have the boiler commissioned by a trained professional. Or else it's highly likely you will have major reliability problems.
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@SuperTech I think your critique is fair, but I wanted to offer the counter argument, as I think there are situations where combis are the better option, all things considered.
Our home is on the small side (1,200 SF) and we do not have a basement. The mechanical room (which is really just a closet with two B-vents) is located right off the living room. The contractor who built the place in the 1990s installed a Burnham Minuteman which is a cast-iron boiler with a tankless water heater coil. The Minuteman is a sizable boiler and the install itself was pretty sloppy, so it takes the lions share of the 6' x 4' mechanical room. It's also quite noisy … fine for a basement, not so great for a single floor building.
The MinuteMan lasted at least 30 years before the heat exchanger started to rust out. It probably could have lasted another 10 years with better maintenance and more attention to return temps. Anyhow, I am in the process of replacing it with a wall-hung Burnham Alta. This install is going to take up about 25% of the space, will be far more quiet, and a lot more fuel efficient.
Do I expect the Alta to have a 30 year lifespan? Not really. I also know it will need more regular maintenance than what it's replacing. All that said, the benefits of getting space back in that room, a much quieter install, and higher fuel efficiency makes it a great option for us.
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i have owned and lived with a few different combis now, 16 years on one
The key is knowing the heat load and dhw requirements
A 120-150k is often adequate for average dhw production? So a 15,000 low end, not many cast or copper boilers go that lowCycling is not much different than a tankless water heater
Water conditions and servical interval are important
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
That's the start of it, yes. But anything down the line as far as error codes, troubleshooting, etc is like a pager in a sea of iPhones. Super archaic and very difficult to navigate
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@GroundUp Gotcha. That is a little disappointing … I also purchased their USB Connect device, so fingers crossed that helps the experience a little bit. A stretch goal was to use USB Connect to fetch data into a dashboard, or pull off smart home integrations. We'll see … if the interface is archaic that may be a non-starter.
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@hitchum - I installed a HTP UFT 80K BTU boiler with an indirect DHW tank in my home. Not advocating for indirect over combi just relating my experience with the HTP boiler which was (and continues to be) quite good. I found their controls to be pretty easy to configure (with some very good guidance from @Ironman).
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My non-expert opinion would be lochinvar, htp, or viessman. viessman's simpler stuff is price competitive.
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I've had good luck with condensing tankless units with plate hx for space heat. As long as your water is not hard, they are pretty low maintaince and work well. Bonus is while space heat is running, you won't get any of the cold water slug or delay issues typical of combi/tankless. You do need a more expensive high head pump to move enough water through the tankless though.
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