BOSCH 125X flame intensity

[GlenJ]

Long winded question here:

Bosch Aquastar 125X NG, purchased in 2001 & working great until recently. I’ll admit to a lack of maintenance on my part. Never descaled until last week, but again, I never had issues until last 2 winters.

The facts: Single story ranch-style home, 1 shower over tub, 1 bathroom faucet, 1 kitchen faucet, 1 Washing machine. Located in San Jose California, very moderate climate. The washing machine is nearest to the water heater (WH), next is the kitchen faucet, then the shower and finally the bathroom faucet. All pipes are copper and the incoming pipes (to bathroom) are insulated.

WH works like a champ in the spring, summer and fall, but winter is when the issues occur. When I run the shower only, the best water temp I can achieve is 84°, but if I “add” the kitchen faucet on full hot, the shower temp rises to a reasonable 100-105°. The incoming water temp is 55°, and the psi at an outside spigot is 80psi.

Individual gpm (@ full hot) in kitchen is almost 2 (1.914), and gpm at tub spigot is a bit over 2 (2.608). Combined (kitchen and tub on full hot simultaneously) is: Kitchen 1.45 gpm and tub 2.165 gpm.

What part of my WH ‘triggers’ the flame height/intensity? It seems as if there are 4 flame levels…small (about 1”), med (2”), lg (3”) and XL ( 4”). LOL, not very technical, I know! If this was an issue in the warmer months, I’d conclude my WH was dying, but the darn thing runs great other than wintertime.

Perhaps my water pressure is too high, and is flowing ‘too fast’ through the WH, thereby not giving the water a chance to absorb the heat. Just a thought. I’ve yet to replace the water valve, though I will if that’s the only (or best) solution. Are there any adjustments I can make to the WH? Again, it seem to be a flow vs heat rise (flame height?) issue. And why only in the winter?

Thanking you in advance! Glen

 

[Stuff]

Valve rebuild kit may not fix it but is supposed to be replaced every few years.
http://www.houseneeds.com/repair-parts/bosch-aquastar-125x-water-valve-rebuild-kit-wvkit125x

Might be something in one of the technical bulletins:
https://www.bosch-climate.us/bosch-...rvice-bulletins/38b-125-series-bulletins.html

 

[Sponsor]

 

[GlenJ]

Thanks for the reply & advice Stuff!
I've dug deep into those Bosch technical bulletins, and while they are an awesome resource (even written for the layman like me), I've yet to find one that addresses my specific issue. Reading "between the lines", I have an idea that my water pressure might be to high, but I was hoping that someone else here may have seen this problem before.
And yep, I'm figuring a new water valve is in my future, but I'm (foolishly) holding off until I've tried everything else.
Thanks!

 

[Stuff]

I've got the older 125B and replaced the filter once. I bought the valve rebuild kit years ago and it is sitting on the shelf waiting for a need.

Does the temp go down if you rotate the knob? Maybe check the setting referred to in step 5 of the G1-07 bulletin.

 

[GlenJ]

Interesting that you mention that G1-07 bulletin...a few hours ago adjusting that very 'adjuster' as per those instructions.
The slot was in the vertical position (factory setting?), so I rotated it to the horizontal...no improvement, though if I interpret the bulletin correctly, the horizontal position is for a lower heat setting. Not too sure though...

As for the knob itself, I rotated it counterclockwise and couldn't see any noticeable decrease in the flame height/intensity, though the water temp did lower 2-3 degrees at the tap. BTW, how far should you be able to rotate the knob in the counterclockwise direction? I didn't notice a 'stop', and of course didn't want to keep turning it too far!
Thanks again for all your suggestions!

 

[Stuff]

Just checked on my 125B. Goes not quite 360º to get to the stops. Strange but lowest setting counterclockwise is about 8 o'clock and then go clockwise until about 7 o'clock. Easy to turn. A but tighter than a kitchen faucet handle.

 

[Dana]

Every 2gpm is about 1000 lbs/hour. The BTU rate is the temperature rise x lbs/hr. The max firing rate on that thing is 117KBTU/hr in / ~93K-out

So if you're looking for 110F water (tub-filling hot, not scalding) and your wintertime incoming water temperture is say, 50F, that's a 60F difference and, so the most it can deliver is 93,000/60F= 1550lbs/hr, which is about 3 gpm. If your incoming water temps are under 50F, it'll be less than 3gpm.

That's it. Anything more than that it won't have enough burner to support that flow.

 

[GlenJ]

Every 2gpm is about 1000 lbs/hour. The BTU rate is the temperature rise x lbs/hr. The max firing rate on that thing is 117KBTU/hr in / ~93K-out

So if you're looking for 110F water (tub-filling hot, not scalding) and your wintertime incoming water temperture is say, 50F, that's a 60F difference and, so the most it can deliver is 93,000/60F= 1550lbs/hr, which is about 3 gpm. If your incoming water temps are under 50F, it'll be less than 3gpm.

That's it. Anything more than that it won't have enough burner to support that flow.

Thanks for doing the math Dana (I was never very good at it...). It all makes sense looking at those numbers.
What still has me scratching my head is: Until a few years ago, the WH was working great regardless of the season. Winter, fall, etc...no issues.
At first I thought my municipality was lowering the water pressure during the winter, but that wasn't the case.
Probably gonna answer my own question here, but it's likely due to a lack of maintenance on my part. No one else to blame (although the installer never told me about the annual descaling).
Last week I descaled it as per the Bosch bulletin, and while I did get a small amount of sediment flushed out, I suspect the water valve is restricted and needs replacement.
Have you (or anyone) had good results with the replacement "poly" (plastic) water valves?

 

[Dana]

If the water pressure is lower, the flow is lower, and it should be better able to keep up. Perhaps the water pressure has gone up? What is the water pressure at your house?

Annual descaling is usually only necessary the water is fairly hard. If you're getting water from the city the water department usually monitors and reports the water hardness levels, but most city water in the Bay Area isn't too bad. I used a similar water heater with comparable output for 14 years from a city water supply for 14 years without it liming up. (It was retired working when I upgraded the heating system, which now heats the domestic hot water too.) Given that the wintertime incoming water temperatures are regularly sub-40F at the low point, you can bet I was pretty clued in as to it's capacity during the winter months! (We had to schedule showers to not coincide with clothes washing, etc.)

 

[Stuff]

The problem isn't with BTUs as OP said that temp rises to an acceptable level with more flow (adding sink). From that it sounds more like the regulator isn't turned up high enough as the Bosch 125 series isn't temperature regulated, but by flow. So one easy option could be to replace the shower head with a higher flow version.

From the manual:
During the colder months, or in cold climate areas, it might be necessary to set the control to the maximum position, all the way clockwise to the right.

 

[GlenJ]

If the water pressure is lower, the flow is lower, and it should be better able to keep up. Perhaps the water pressure has gone up? What is the water pressure at your house?

Annual descaling is usually only necessary the water is fairly hard. If you're getting water from the city the water department usually monitors and reports the water hardness levels, but most city water in the Bay Area isn't too bad. I used a similar water heater with comparable output for 14 years from a city water supply for 14 years without it liming up. (It was retired working when I upgraded the heating system, which now heats the domestic hot water too.) Given that the wintertime incoming water temperatures are regularly sub-40F at the low point, you can bet I was pretty clued in as to it's capacity during the winter months! (We had to schedule showers to not coincide with clothes washing, etc.)

Dana, the water pressure at an outside spigot (bib?) is 80psi, which seems high to me. The owner manual for the 125X recommends 30-50 psi for installation on a well system. I'm on city water, so I'm unsure if that makes any difference. Psi is psi, right?
I'm considering having an adjustable pressure regulator installed.
Thanks SO much for all the feedback. I'm trying to avoid replacing the WH altogether.

 

[GlenJ]

The problem isn't with BTUs as OP said that temp rises to an acceptable level with more flow (adding sink). From that it sounds more like the regulator isn't turned up high enough as the Bosch 125 series isn't temperature regulated, but by flow. So one easy option could be to replace the shower head with a higher flow version.

From the manual:
During the colder months, or in cold climate areas, it might be necessary to set the control to the maximum position, all the way clockwise to the right.

Thanks for the input Stuff!
As I have the regulator turned up to the maximum, my next semi-logical conclusion is the regulator itself is corroded internally. Looking at page 13 of the owner manual: troubleshooting > water is not hot enough > 6. "Parts in the water flow valve are corroded so that the gas passage is not fully opening"

I'd also like to check the Btu input, but I don't mess with gas. I'll DIY plumbing, electric, most anything...but not gas.

 

[Stuff]

For BTU input you can clock the gas meter. Roughly 1000 BTUs per cubic foot. From your bill you should find the therm multiplier as a correction factor.

 

[GlenJ]

Welp…my WH just “ made a decision “ for me.
I was set to purchase a new water valve, but before I plunked down the money (nonrefundable), I wanted to make sure I could remove the old one. There is a considerable amount of corrosion on that aluminum housing, especially around those two retaining screws. Well, the screws are indeed seized and the slots in the Phillips head are so soft that they are unusable as well. Penetrating oil, CLR, even baking soda and vinegar on a toothbrush, but it’s seized completely.
It’s sad something so small and minor is the reason I am replacing the WH, but that’s the way goes. I got a good 17 years out of it!
I really really want to thank those of you who gave me suggestions and ideas. This is a great forum and I sure learned a lot!

Happy holidays to all!
Glen

 

[Dana]

Most simple tankless units like that will go 20-25 years, but 17 years "working-mostly" isn't exactly infant-mortality either. A lot depends on how much and the quality of the water and fuel went through it over it's lifespan, the cleanliness of the combustion air, etc.