Indirect water heater running out of hot water.

7 years ago

I installed a Brockford White RTV-40-L stainless steel indirect water heater alongside our new Slant/Fin VSPH-90 90k btu boiler two years ago. We've never been happy with how quickly we run out of water (just the two of us, reasonable shower times), and we want to put in a bigger bath, but our small 40gal bathtub runs out the hot water filling it up (sometimes not even full).

I did some measuring tonight. No hot water to speak of run before this today. The water coming out right way was ~120*. I measured 5gpm at my tub faucet. After 3min and 15gal, the water was down to 95*, too cold for a shower or bath. After 7min and 35gal the tub was full of 93* water. 68* water had been coming for a few minutes- maybe the temp coming in from the meter. Something seems wrong with this situation.

After 30min the temp at the faucet was back up to 130*. I think my override might be wired wrong (to shut off house heat while the water heater's heating), but that shouldn't have anything to do with the situation above. The aquastat dial on the water heater says 100*, but it's mounted on the bottom half, so I suppose that's measuring the cooler water toward the bottom? I could turn it up and make that initial water ~150*, maybe install a mixing valve, but something seems wrong about only 15gal of hot water coming out of a 40gal heater. I think everything's plumbed right- the cold inlet is at the bottom, so there's no chance I switched them, and I don't think there's a stand tube to be broken off in a model like this.

This last paragraph is a long shot and likely unrelated: when I installed it, I overtightened the lower boiler return fitting and it still wouldn't stop leaking, and when I tried to unscrew it something unscrewed inside the water heater at first because I couldn't get a wrench on the nipple coming out. There was pressure on at the time and I heard the water screeching, presumably going through some internal connection from the house pressure into the boiler circuit, before I tightened it again and it stopped. I took apart the water heater skin to get a wrench on the nipple and fixed my problem. I talked to both Brockford White and a local plumber about that, and the vendor didn't seem to think there was even a threaded connection inside there (there must be). Neither of them seemed concerned anyway. And I've shut off house pressure and turned on a hot faucet for a while- if there was a leak between the boiler circuit and the house pressure part of the heater, it would drain down my boiler pressure (no auto-feed), which it doesn't.

Any ideas?

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Comments (4)

armoured
7 years ago
You might want to check the product manual and suggestions there in the trouble-shooting guide.

http://www.bradfordwhite.com/sites/default/files/product_literature/238-46392-00G.pdf

See troublehooting on pg 32-33. My top guesses would be boiler not set to prioritize hot water, and/or faulty aquastat. Possibly sediment or scaling in the tank contributing? There are annual maintenance suggestions there, best bet may be to get someone out to do the maintenance and at the same time explain the problem and see what they come up with. Don't know how much the aquastat (thermostat) costs, but may be best to have them change it out just to rule out that as a possible cause. (Don't know how difficult it is to do this yourself...)
ericsanford69
Original Author
7 years ago
last modified: 7 years ago
I had a conversation with a local pro, and he believes adding a mixing valve and turning the aquastat up from 100* to something like 140* will do wonders. He said it's normal in any water heater to have much higher temps at the top and lower at the bottom, with the average around the aquastat setting, meaning we have ours turned way down. I'll give that a try.

On the DHW priority wiring, I'm having a little difficulty finding straightforward info. Most diagrams/discussions include so many references to controllers and various models of components that I can't tell what the basic schematic should be. Here is my current setup:
We have a single circ pump controlled by the boiler control. I just learned that the "DHW End Switch" terminal in my boiler goes to the HydroStat controller and only bypasses the thermal targeting in order to get full power from the boiler during DHW demand. My plan now is to simply add a DPDT relay (in red below) with the coil powered by the aquastat, that disconnects the signal to the two heating zone valves from their thermostats. This will will close those valves while the DHW is heating and create the priority setup. Anyone see any problems with this setup?
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Vith
7 years ago
last modified: 7 years ago
120 is the mfg setting normally used, 140 might work but it might make your T&P valve go off also so keep an eye on that.

There are scalding risk with setting too high, and pathogen risks setting too low.

http://lifehacker.com/whats-the-best-temperature-for-my-water-heater-1465372005

The reason the temp is lower at the bottom is that is where the water comes in as cold, if a tank sat there unused the temp would balance out.

Ensure your plumbing and electric is correct, page 21 of armored's link is the plumbing.

As far as electric, check page 17 in link below and consider the water heater as its own zone with its own thermostat (the aquastat).

https://www.slantfin.com/wp-content/uploads/2016/01/VSPH-Install-Guide-and-User-Manual-Pre-DOE-2012-207.pdf

I would make sure your electric and plumbing is connected correctly before you set higher than 120.
ericsanford69
Original Author
3 years ago
Following up on this, I did install a mixing valve and turned the aquastat up to 140. It's been working like a charm for the last three years. I also realized later on that my DHW priority wasn't wired right and needed a relay. This is how it's set up now:

Indirect water heater running out of hot water.

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armoured

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Indirect water heater running out of hot water.

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armoured

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