Commercial Water HeatersGas Storage-Type Instantaneous
BOCK OT800*-A Commercial Water Heater Manual
Setup, everyday use, maintenance and troubleshooting for the 130-gallon commercial storage-type instantaneous gas water heater, with verified specifications.
- Input800,000 Btu/h
- Thermal efficiency98%
- Storage130 gal
- FuelNatural gas or propane
About the BOCK OT800*-A
BOCK model OT800*-A is a 130-gallon commercial storage-type instantaneous gas water heater that meets ENERGY STAR efficiency requirements for commercial water heating. It is rated at an input rate of 800,000 Btu/h and a thermal efficiency of 98% and runs on natural gas or propane. That efficiency is higher than 91% of the 47 Gas Storage-Type Instantaneous models in our database.
At 98% thermal efficiency this is a condensing water heater: it extracts enough heat from the flue gases that water vapor condenses inside the heat exchanger. That is why it uses plastic or stainless venting, needs a condensate drain and is typically vented with a fan.
It has 130 gallons of storage. Rated standby loss is 1,500 Btu/h.
Specifications
| Brand | BOCK |
|---|---|
| Model number | OT800*-A |
| Type | Gas Storage-Type Instantaneous |
| Fuel | Natural gas or propane |
| Input rate | 800.0 kBtu/h |
| Thermal efficiency | 98% |
| Storage volume | 130 gal |
| Standby loss | 1,500 Btu/h |
| Vent pipe size(s) | 6 in. |
Safety information
- Installation, gas piping, venting and service must be performed by a licensed plumber, gas fitter or qualified heating contractor in accordance with the National Fuel Gas Code (NFPA 54) or CSA B149.1 in Canada, local plumbing and mechanical codes, and the manufacturer's installation manual.
- Incorrect venting or combustion air can cause carbon monoxide (CO) poisoning. Use only the vent materials, lengths and terminations the manual permits, and install CO alarms in the building as required by code.
- Do not store or use gasoline, solvents or other flammable vapors near the water heater.
- A temperature and pressure (T&P) relief valve of the correct rating must be installed, with its discharge line run full-size to a safe, visible drain point. Never cap or plug the T&P valve or its discharge line.
- Water above 120 °F (49 °C) can scald. Where water is stored hotter for sanitation or Legionella control, install thermostatic mixing valves to temper water delivered to fixtures.
- Turn off the fuel or power supply and close the water valves before servicing.
Installation and first-time setup
Commercial water heaters must be sized to the building's peak hot-water demand and installed to the manufacturer's instructions. At 800,000 Btu/h, this model needs gas piping and a meter able to supply roughly 800 cubic feet per hour of natural gas (based on about 1,000 Btu per cubic foot) in addition to every other appliance on the line, at the inlet pressure listed on the rating plate.
- Plan the location
Place the unit on a level, noncombustible surface, near a floor drain, with the service clearances shown in the manual. Use a drain pan where a leak could damage the building.
- Connect the water piping
Install full-port isolation valves and unions on the cold inlet and hot outlet. Where a backflow preventer or check valve creates a closed system, add a properly sized thermal expansion tank.
- Connect the gas supply
Run gas piping sized for the full input rate, with a manual shutoff valve and a sediment trap (drip leg) ahead of the appliance gas valve. The model line is offered for natural gas and propane; confirm the gas type on the rating plate matches your supply — conversion must be done only with the manufacturer's kit by a qualified technician. Leak-test all joints with an approved solution, never a flame.
- Install the venting
Use only the vent and air-intake materials, diameters and maximum equivalent lengths in the manual (the certification lists 6 in. vent pipe), slope horizontal runs back toward the unit so condensate drains, support the pipe as specified and keep terminations clear of windows, doors, air intakes and snow lines.
- Connect the condensate drain
Route the condensate drain to a suitable drain through a condensate neutralizer where required by code or the manufacturer — condensate from gas combustion is acidic and can damage drain piping. Protect the line from freezing.
- Provide electrical power
Connect the electrical supply for the controls, igniter and blower as shown on the wiring diagram, with a service disconnect.
- Fill and purge before firing
Fill the tank completely and open a hot-water fixture until water flows steadily with no air. Never fire the burner with an empty or partially filled tank.
- Commission with a combustion analysis
A qualified technician should start the unit, verify gas pressure, check combustion (CO and CO2 or O2) at high and low fire with a calibrated analyzer and confirm all safety controls operate.
Using your commercial water heater
Setting the water temperature
Choose the storage or outlet temperature for the application and the facility's water-management plan. Common practice for Legionella control is to store water at 140 °F (60 °C) or higher and deliver it to hand sinks and showers through thermostatic mixing valves at a safe temperature. Commercial dishwashers usually need 140 °F supply water, with a booster heater for a high-temperature sanitizing rinse.
Recovery capacity
Based on its input rate and 98% thermal efficiency, this unit can heat roughly the following amounts of water per hour (calculated estimates; the manufacturer's recovery table governs):
| Temperature rise | Approximate recovery |
|---|---|
| 40 °F | 2,353 gal/h |
| 70 °F | 1,345 gal/h |
| 100 °F | 941 gal/h |
During a peak, usable hot water is about 70% of the 130-gallon tank volume plus the recovery during the draw period. If demand regularly exceeds this, consider additional units or storage.
Operating controls
Modern condensing commercial water heaters use electronic controls with a display for setpoint, diagnostics and lockout history. Lockouts after repeated ignition failures are a safety feature — find and correct the cause rather than repeatedly resetting the control.
Care and maintenance
| When | What to do |
|---|---|
| Every month | Check for leaks, verify the temperature reading, and make sure the vent and air intake terminations are clear of debris, snow and nests. |
| Every 3 months | Drain a few gallons from the drain valve to flush sediment; in hard-water areas flush more often. Manually lift the T&P valve lever briefly (if the manufacturer permits) to confirm it opens and reseats — be ready for hot water. |
| Every 6–12 months | Inspect and clean the condensate trap and drain, and replace neutralizer media when it is depleted. |
| Every year | Inspect anode rods if the tank uses them and replace when heavily consumed; check the tank for corrosion. |
| Every year | Have a qualified technician inspect the burner, igniter and flame sensor, clean the combustion air filter or screen, inspect the vent for leaks and support, and repeat the combustion analysis. |
Follow the maintenance schedule in your manufacturer's manual — intervals depend heavily on water hardness and usage — and keep a service log; it is often a warranty requirement.
Troubleshooting
Check fuel or power, water valves and settings first. Anything involving gas controls, combustion, venting or electrical components should be handled by a qualified technician.
| Problem | Possible cause | What to try |
|---|---|---|
| No hot water, control in lockout | Gas supply off or low pressure; blocked vent or air intake; blocked condensate drain; failed igniter or flame sensor. | Check that the gas valve is open and other gas appliances work; clear vent terminations; check the condensate trap; note the code and call a qualified technician. |
| Not enough hot water | Demand exceeds storage plus recovery; setpoint too low; mixing valve misadjusted; sediment reducing capacity. | Compare peak demand with the capacity tables above; check setpoint and mixing-valve settings; flush the tank. |
| Water temperature fluctuates | Mixing valve sticking or misadjusted; recirculation flow or balancing problems; control setpoint differential. | Service or adjust the mixing valve; check the recirculation pump and balancing valves; review control settings. |
| Water leaking from the condensate line area | Blocked or disconnected condensate trap or drain. | Clear and reconnect the trap and drain; check the neutralizer for clogging. |
| T&P valve discharging | Excess pressure from thermal expansion; setpoint too high; faulty valve. | Check the expansion tank charge and size; verify setpoint; replace the T&P valve if it leaks at normal pressure. |
| Rumbling or popping sounds | Sediment on the tank bottom or heat exchanger. | Flush the tank; if noise continues, have the heat exchanger inspected. |
| Error code displayed | Brand-specific diagnostic code. | Error codes are not standardized; consult the code table in your manufacturer's manual before resetting. |
Energy use and running costs
Heating 1,000 gallons of water by 70 °F (for example, from 50 °F to 120 °F) takes about 583 thousand Btu. At 98% thermal efficiency the BOCK OT800*-A burns roughly 6.0 therms to do it — about $8.93 at an assumed natural gas price of $1.50 per therm.
| Hot water per day | Gas per year | Cost per year |
|---|---|---|
| 250 gal | 543 therms | $814 |
| 500 gal | 1,086 therms | $1,629 |
| 1,000 gal | 2,172 therms | $3,258 |
| 2,000 gal | 4,344 therms | $6,515 |
At full fire the burner uses 800,000 Btu/h, or about 8.0 therms per hour ($12.00 per hour of continuous firing).
The rated standby loss of 1,500 Btu/h represents the heat the tank loses while holding temperature. Over a year that is roughly 131 therms ($197), before burner efficiency is accounted for — insulating hot-water piping and controlling recirculation keep these losses down. That standby loss is lower than 28% of the 47 Gas Storage-Type Instantaneous models in our database.
If you run the unit on propane, multiply the therm figures by your propane price per therm (one gallon of propane contains about 0.915 therm).
Frequently asked questions
What is the input rate and efficiency of the BOCK OT800*-A?
It is rated at 800,000 Btu/h input with a thermal efficiency of 98%, so about 784,000 Btu/h ends up in the water at full fire.
What is the recovery rate of the BOCK OT800*-A?
Calculated from its rated output, it can heat about 941 gallons per hour at a 100 °F rise, or about 1,345 gallons per hour at 70 °F. Check the manufacturer's published recovery table for exact figures.
How many gallons does the BOCK OT800*-A hold?
It has a storage volume of 130 gallons.
Can the BOCK OT800*-A run on propane?
The model line is certified for both natural gas and propane. Confirm the gas type on the rating plate, and have any conversion done by a qualified technician with the manufacturer's kit.
How much does it cost to heat water with the BOCK OT800*-A?
At 98% thermal efficiency, heating 1,000 gallons by 70 °F takes about 6.0 therms — roughly $8.93 at $1.50 per therm.
Is the BOCK OT800*-A ENERGY STAR certified?
Yes. It appears on the ENERGY STAR list of certified commercial water heaters, with a certification date of August 2026.
Sources and disclaimer
Specifications on this page come from the ENERGY STAR certified commercial water heaters dataset published by the U.S. Environmental Protection Agency (record certified August 10, 2026), retrieved October 7, 2026.
The setup, operating, maintenance and troubleshooting guidance is written by ManualHarbor's editors for this specific product type and configuration. It is an independent guide — not a reproduction of the manufacturer's manual — and ManualHarbor is not affiliated with BOCK. Always follow the safety instructions, installation requirements and warranty terms supplied with your unit, and contact BOCK or an authorized service provider for warranty repairs and replacement parts.
Running-cost figures use assumed U.S. average utility prices and are estimates for comparison only. See our editorial methodology for details.
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