? how to force Buderus indirect above 140 ?

[000utback]

Buderus S32 indirect water heater powered by Buderus GB142 boiler. I want to take the water heater to 165F to kill sulphur bacteria. Specs say it's rated to 203. The control knob on the boiler (BC-10 module) maxes at 140. How can I get it to go higher? It looks like I could put a jumper across the water tank temperature wire where it connects to the BC-10, but 1) how can I read the temperature (currently have thermometer tape on hot water outlet) and 2) how can I get it to maintain 165 overnight?
The elevated temperature idea looks great, until I found out my fancy electronic controls are limited - indubitably to avoid lawyers.
If it matters, this unit also has the AM-10 outdoor reset control. And, the boiler is set to provide 190F water to the water heater.
Any and all comments will be appreciated.

 

[Phog]

One option would be to setup the water tank as a standard heating zone (priority) via an external boiler call. Instead of using the boiler's built-in DHW feature, as you appear to be now. Then you can set the new "zone" to whatever temperature you like. This would probably require purchasing & installing additional equipment. Finally this is not a matter to take lightly. 165F is an extremely dangerous temperature to have your water tank set at. Even temporarily. One mistake could severely burn someone. I don't believe tempering valves are considered sufficient as anti-scald protection. There is a reason that 140F is the highest temperature your boiler allows you to set. Have you considered killing the SRB a different way such as chemical disinfecting?

 

[Sponsor]

 

[Dana]

In most areas codes require a thermostatic mixing valve or tempering valve between the water heater and any water supplies to mitigate the scald risk, even though it's not 100% risk free. A discussion of the topic lives here.

 

[Jadnashua]

FWIW, my indirect tank says the max temp of the tank is designed to be 140-degrees, so increasing it above that, at least for my tank, is not advised. Check the specs on the one you have before trying to figure out a way to make it hotter...it may not work out well!

 

[000utback]

Thanks for the comments.
If I set up the DHW as a separate heating zone, it will be limited by the temperature of my outdoor reset control - which hardly ever runs the boiler over 140F. The DHW connection on the boiler has a different setpoint (180-190F) than the space heating function (outdoor reset temperature). So I have to use the DHW connection to get 190F supply temperature to the water heater. I was looking for some kind of existing control, perhaps known only to professional installers or gurus, to use the existing controls to drive the temperature up. Once a month, drive the temperature up overnight, go down in the morning and drain some hot water so cold tempers the tank, and be good to go. Hey, I reckon I can de-select the outdoor reset and set the boiler temperature to what I want (e.g. 170), then jump the DHW temperature so it forces on the circulation pump to the DHW, and gives boiler a call for heat. Then it would circulate through the heating coil/boiler for as long as it's jumpered, but never exceed the boiler control temperature of 170. The boiler itself would be modulating and firing as needed to maintain the 170 on his side. That's not too hateful for a monthly pm.

The DHW tank specs are very clear on the 203F max.

Yes, there is an antiscald valve. Initially though I wouldn't trust it. I would lock shut the valve to the house while I do this, to assure that I put things back where they should be before I allow hot water into the house.

I'm looking at the chemical disinfectants, and did a Cl flush over the weekend. I will have H2OH on hand for the next time. The domestic side of the heater is piped with PEX, so I could add a valved chemical port if I want to dose it regularly. Using heat and the existing controls would have been easier, if they allowed the range.

I'm comfortable with the heating in place idea, cuz I did that in food processing plants for 15 yrs. The 160 heating recommendation is repeated by Wisconsin DNR, Minnesota health department, etc. The H2OH treatment is quoted 50x more often. I think I'll try peroxide for the season and see how we do. Seems safest.

My new powered anode arrived today, and that should be a big step in fighting the sulfur odors.