Polaris water heater problem & replacement

[jtech1]

I have a Polaris PBG102-50T100-2N that I put in service about 12 years ago. It has been having an issue for quite a while... from inside it sounds like just a whoosh at ignition (not even obvious that it is an issue from inside sound). But, from outside (which I did not know until I happened to be under the PVC vents last week) it sounds like a backfire or gunshot. From what I can tell, that indicates a delayed ignition. I am going to have an HVAC tech come out with a manometer and check the gas pressure and gas valve. Is there anything else that could cause this? Could an issue with the in or out vent, or burner needing cleaning cause this?

Is it possible that it could be fixed with just a service call and adjustment or am I likely looking at a new gas valve or burner?

Any safety issue?

At what point is it better for me to just replace the unit? Since it is already out of warranty... and even a stainless steel tank will not last forever.

And if I want to replace it, what are my best options today? This is a 100,000 BTU, 50 gal, direct vent, condensing unit. We have not had ANY problem with the water it provides, except that we could never fill our large master bath tub before the hot runs out. So, I either need a larger unit (BTUs and/or gallons)... OR, a smaller unit and put some point of use electric heater at the master bath tub (I do have #6 wire I ran there for a future steam unit for shower that I never installed). My only requirement is that it is direct vent/sealed combustion if gas. But I am open to other non-gas options if they would meet our needs. 3-1/2 bath house. Aside from master bath tub, no other big hot water uses. I do also have a passive siphon recirc line on the hot side also... to keep hot water at the farthest fixtures at all times.

I would appreciate any advice!

 

[jtech1]

I should add that the backfire does not happen every time it starts up. Only now and then. But there is always the hard whoosh sound both inside and outside... and, when it starts up with the whoosh, a small amount of condensation shoots out the vent pipe outside.

 

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[jtech1]

Any input on the Polaris delayed ignition issue would be greatly appreciated.

I have been looking at tankless options in anticipation of having to replace the Polaris at some point. The Bosch Greentherm 9900iSER looks like a pretty good unit. I could reuse the existing direct vents, top water connections, eliminate the external passive recirc and plumb my recirc line into the Greentherm and let it's internal recirc pump do it's thing. I have geothermal heat and a pre-heat tank off that, so in the summer, incoming water will be at least 100 deg, and I should be able to get 9-10 gpm at 140 deg out of the tankless. Winter I would either need to keep my geothermal desuperheater on (my unit will do that) and pay the cost for that, or accept the flow rate reduction to around 4-5 gpm with incoming water at 55 deg. Actually, I assume that since it will sit in my basement preheat tank, it will gain some heat while there... so may be 60-65 deg? I have well water, low TDS, and pH and softener in the system.

It seems like a pretty easy install... other than flow concerns, is there anything else I am missing here that could cause me issues or concerns?

 

[Jadnashua]

Have you measured your actual wintertime incoming cold water temps? Your pressure tank may help temper things for a bit, but once it's all just coming out of the ground, it could be lots colder. My incoming cold water actually reaches just over freezing after a cold snap. You're a hundred or so miles south, so things would tend to be a bit warmer, but not as much as you think.

 

[jtech1]

My geothermal tells be the incoming water temp... this time of year it stays around 50 deg.

On the delayed ignition question... another possible piece of the puzzle... or may be unrelated... after ignition, if I sniff around the gas control, I get a faint gas smell. I know there is no leak in the gas connections, since I have retested all with soapy water and get no leaks at all. And I don't smell any gas if it sits there without running... so, what would cause it to have a faint gas smell for a period of time after ignition?

 

[Jadnashua]

I'd guess if the gas runs a bit before it ignites, some raw gas could get into the exhaust. Once the main flame does ignite, it might then ignite what's in the exhaust, which may be the source of your noises. Once things are running, though, you should not smell raw gas.

Does the fan turn on at the proper time? The manual should describe the proper sequence. There's usually a pressure/vacuum switch that decides if the fan is actually running enough to make the mixture proper. Sometimes, the hose going from the switch to the sensing point can split and the resulting leak can make things operate a bit wonky. IF that happens, it often happens where it is stretched over the nipple, but if it rubs against something along its path, it could wear a hole in it.

 

[jtech1]

Thanks, Jim. I will check that. The vent motor comes on for 5-6 seconds... then shuts off... then 30 seconds later it comes on again and ignites. My understanding is this is normal operation. At the ignition time is when I get the smell for a while... it does not seem to get worse while running... and dissipates once it stops.

The power vent is on the bottom of the tank on the Polaris... and inside the panel (inside shroud at bottom of tank), there is air movement while running, which I believe is only from the motor coils and not intake or exhaust air since those are sealed to the PVC vent pipes.

I do see some hoses running from intake area to gas valve and somewhere else... I will check those carefully for any cracks.

 

[Jadnashua]

The initial fan period is designed to ensure there's no raw gas in the chamber prior to starting the sequence of ignition. You only want a controlled fuel/air mixture when you're trying to start up the flame.

 

[jtech1]

I don't see any obvious leaks in the tubing going to the pressure switch. I do see a small metal tube from the gas valve to somewhere behind it. Is that the path of the gas from the valve to the burner? I can't find a schematic showing the exact path. Trying to determine what points the gas could be coming from. Looks like there is both a small blower gasket, and a larger burner gasket. These possible leak points I assume... how about through the blower motor... if the blower side sealed from the motor side? I assume is the blower is operating, gas and combustion fume should not be backing up toward the blower... only forward through the condensing system and outlet vent.

Would be nice to find out the exact sequence of blower, gas, igniter, etc. blower first, then igniter, then gas? or other?

 

[Dana]

Filling big tubs with a tankless is an exercise in tedium. Tank water heater output gpm rates are limited by the water pressure and plumbing sizes, and far more satisfactory for filling tubs. How big is the tub you need to fill? Would an 80 gallon cover it?

The 80 gallon HTP PH76-80 with a modulating 76K burner would cover most soaker-tubs, but not necessarily a bigger spa type tub. The 3:1 turn down ratio make it a bit like a tankless when serving up serial or overlapping multiple showers.

If an 80 gallon heat pump (electric) water heater can fill the tub it may be more appropriate than gas, especially if it's located in a damp basement that needs a dehumidifer running all summer to keep the "musty basement" smell at bay. But unlike the PH76-80 it can't deliver the "endless shower" experience with 5+ people showering per hour.

 

[jtech1]

Thank you all for the input.

jadnashua (or others): any details about questions two messages up would be appreciated.

Dana: I have not ruled out a tank WH to replace the one I have... but, I guess I am trying to understand WHY a tankless makes filling a big tub an issue? I have 1" main pipe from basement to master bath with soaking tub (around 80 gal). If my geothermal preheat tank is at 100 deg, and I only need a 30-35 degree rise at the tankless, the Bosch 9900iSE will deliver 11.2 gpm... mixing with 30% cold at tub, that should give me a fill rate of around 14-15 gpm, and take about 5-6 minutes to fill the tub. What am I missing?

 

[Dana]

Thank you all for the input.

jadnashua (or others): any details about questions two messages up would be appreciated.

Dana: I have not ruled out a tank WH to replace the one I have... but, I guess I am trying to understand WHY a tankless makes filling a big tub an issue? I have 1" main pipe from basement to master bath with soaking tub (around 80 gal). If my geothermal preheat tank is at 100 deg, and I only need a 30-35 degree rise at the tankless, the Bosch 9900iSE will deliver 11.2 gpm... mixing with 30% cold at tub, that should give me a fill rate of around 14-15 gpm, and take about 5-6 minutes to fill the tub. What am I missing?

With a tankless the flow is burner output limited. A rate of 11.2gpm = 5600 lbs/hr. The output of a 199K condensing burner is no more than 190,000 BTU/hr at high fire. 190,000/5600= 34F temperature rise, not more. In the dead of winter incoming water temps in NJ can drop to the low 40 F some times/locations it can even be in the high 30s, but for yuks let's call it 45F. So if you like soaking in 78F water, go for it!

A tub fill typically needs 110F water, so with 45F minimum incoming water temp it's a 65F temperature rise. With with the 190K of burner output the best you can do is 190,000/65F= 2900 lbs/hr , 48.3 lbs/minute, or (/8.34 lbs/gallon=) 5.8gpm.

So if it takes 80 gallons to fill the tub you're looking at 80/5.8= ~14 minutes. The only way it'll fill faster than that is a lower temperature, or a bigger burner.

With an 80 gallon tank maintained at 140F and a 1" pipe you can fill it in 5 minutes, or even 3 minutes if you have sufficient water pressure and the pipe runs aren't too long.

 

[jtech1]

With my geothermal unit and storage tank before the tankless water heater, I can get the 50 gal storage tank up to 125 in summer (easy heat from house into storage tank)... and same in winter if it has enough hvac time to run without water usage... so I would say average 90-100 deg in winter with any basic usage/turnover in the storage tank. So the tankless unit would not have to deal with ground temperature water until the storage tank was exhausted.

 

[Dana]

With my geothermal unit and storage tank before the tankless water heater, I can get the 50 gal storage tank up to 125 in summer (easy heat from house into storage tank)... and same in winter if it has enough hvac time to run without water usage... so I would say average 90-100 deg in winter with any basic usage/turnover in the storage tank. So the tankless unit would not have to deal with ground temperature water until the storage tank was exhausted.

The question then becomes why isn't the Polaris @ 140F + geothermal buffer @ ?_?F are not capable of filling the tub? This would take a more sophisticated analysis on where the BTUs are coming from. Just know that at 11.2gpm through the tankless it's not delivering much more than a 34F temperature rise. Also know that at 11.2gpm the pressure drop across the tankless is significant, and may be enough to limit flow to something less than that, whereas the pressure drop across any tank water heater at 10-20gpm is negligible .

With the geo buffer feeding an 80 gallon heat pump water heater the recovery times on the water heater would be acceptably short even in heat-pump-only mode.

If in the end you go with the tankless, don't set it to 140F and mix it down or you'll have issues with temperature control &/or flame-out when operated at low flow. Some condensing tankless units won't even condense with incoming water north of 100F from the buffer- they're designed & optimized for 35-80F incoming water, and some of them shut down when incoming water temps are north of 120F, detected as an error. I have no idea if there is a maximum incoming water spec for the Bosch, but be sure to verify that ahead of time.

 

[jtech1]

Sorry... I did not mention that I just had the geothermal with desuperheater installed. My old one did not preheat domestic HW. But great point about the min water temp that I did not know about. I will need to look into that.

My main drawbacks to replacing my Polaris (which is 100K BTU, 50 gal), is that a new 50 gal (now 130K BTU smallest unit) is over double the cost of the tankless... and NO-ONE in my areas sells or services the Polaris units. Is there another brand condensing, stainless tank water heater I can look at that is similar to the Polaris?

 

[Dana]

Sorry... I did not mention that I just had the geothermal with desuperheater installed. My old one did not preheat domestic HW. But great point about the min water temp that I did not know about. I will need to look into that.

My main drawbacks to replacing my Polaris (which is 100K BTU, 50 gal), is that a new 50 gal (now 130K BTU smallest unit) is over double the cost of the tankless... and NO-ONE in my areas sells or services the Polaris units. Is there another brand condensing, stainless tank water heater I can look at that is similar to the Polaris?

HTP's Phoenix "Light Duty" series are all stainless, with a 76KBTU modulating burner. (Light duty only relative to their bigger-burner commercial water heaters, which come with burners as big as 199KBTU.) The 80 gallon versions run three grand or so at web store pricing but buying direct from HTP may be cheaper. Westinghouse re-brands the same water heaters under their label and support services, which they distribute through Home Depot. They also have stra

Aside from the maximum incoming water temperature issue, there is a minimum firing rate which defines a minimum temperature rise. In the case of the 9900iSE that's about 8500 BTU/hr output. At 0.5 gpm (say washing your hands, and probably the minimum flow rate), is 25o lbs/hr, for a minimum rise of 8500/250= 34F. With an incoming water temp much above 70F that's going to be an issue for a comfortably hot 105F hand washing temperature. With a 100F incoming temp you'd have to crank the flow super high to avoid scalding or flame-out on the tankless. An electric tankless could still modulate low enough, but that presents it's own set of issues.

Does the desuperheater & buffer still preheat when in space heating mode? Would it run enough during the shoulder seasons when there's no heating or cooling load to speak of to keep the water temp high enough for the tankless solution to fill the tub at a reasonable rate?

The operating cost of a heat pump water heater will likely be cheaper than gas in your situation, since even the fraction of the heat taken from the mechanical room is being leveraged at high efficiency by the geo. During the summer it will even lower the cooling load when it runs (putting the heat in the tank rather than into the ground loop) , but backed up by the geo buffer at 125F it's duty cycle would be pretty low.

[edited to add]

An 80 gallon heat pump water heater runs about USD $2K, but isn't stainless. An 80 gallon stainless plain electric tank (no heat pump) runs about half that.

 

[Dana]

Regarding the pressure drop across the Bosch at high flow- looks like at 11.2gpm it's about an 80 psi drop. See Figure 3, p10 of the applications manual. That's a pretty typical curve.

It's possible or even likely you don't even have 78 psi STATIC pressure on the system at NO flow, but measure the static water pressure anyway.

Shall we declare the tankless a non-solution at this point?

 

[jtech1]

I really appreciate you taking the time to help me with this! Great information!

That is quite a pressure drop! I am on well and only have 40-60 to start with... then through pH and softener it drops further. I think you have convinced me I would be much happier with a new tank.

I looked at HTP and it looks like a good fit. I doubt I would miss the 24k by going from 100K to 76K... the extra 30 gal in the tank, I am guessing, would more than make up for it. It looks like it is much easier to service with everything right in the front, as opposed to the Polaris with everything underneath. And the fact that it is modulating would probably save me $ in the long run compared to my Polaris... especially since I have a passive siphon recirc device and the Polaris fires up at full 100k every so often to keep things warm. Do you know if the Westinghouse models at HD are EXACTLY the same parts/unit or if they have cheapened anything for box box sale?

 

[Dana]

I don't know for sure whether Westinghouse has stripped it bare, but I don't think so. I believe it's simply a re-labeling. Scuttlebutt has it that the some of local distributors don't have much in the way of competent tech-line help on their rebranded boilers & water heaters. The sample size is low, and it's all third-hand- can't really vouch for any of the details. (One bad experience multiplies rapidly on the web, even when it's not the real trend.)

Buying direct from HTP may or may not have a unit price lower than web store or a box-store Westinghouse. They understandably prefer to sell & provide technical help to professional installers. That said, they still have fairly open technical support for current owners compared to some.

An 80 gallon heat pump water heater will fill the tub just as fast as an 80 gallon HTP. The recovery times after a tub fill will be longer, but it simply can't/won't short cycle on the recirculation system losses the way a Polaris can. With 80 gallons of buffer you don't really need to worry much about recovery times for other hot water uses, only the patterns of use in the first half hour or hour after the tub fill gulped it most of the way down toward your well water temp. When the geo buffer is preheating the recovery times would still be quite reasonable.

Another other reason to consider heat pump water heater is than NJ has pretty good incentives for solar, which can bring the actual cost of your space heating & hot water even lower. In states where something like a carbon tax has even a remote possibility of passing during the lifecycle of the equipment it's worth considering heat pumps for all major energy use. The utility cost landscape may be changing now that NJ has retreated back into the RGGI fold.

 

[jtech1]

Thanks! I verified with Westinghouse Water Heating (different phone # than HTP but exact same address) that the Westinghouse model is exactly the same as the HTP model... just relabeled. Same warranty. Same parts. I am waiting for call from local dealer for price on HTP model... HD has Westinghouse for around 2700... but 1 month lead time. I think the 80 gal unit will be great for us. Should be easy install... only pain will be rerouting the vent lines without using too many more 90's. I have 3" vent and routed some of it in ceiling to exact drop spots for Polaris... not a big deal... Polaris also has side supply... so I have a bit of work to do on rerouting that to top... but PEX will make that easier than all the copper work I did with the current unit.

I assume these units have not had any major issues or recalls like the Polaris did years back? I have not been able to find any bad news via Google.