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Question DetailsAsked on 8/5/2016

How do I take out a gas hot water heater without blowing my self or house up

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1 Answer


If you are that uncertain how to do it, I would recommend having a pro do it - presumably a plumber, on the assumption a new water heater will be going in to replace it. However, as long as the water heater has a pressure relief valve it is not likely to blow up, and about the only way to even come close to blowing things up is create a gas leak, or to leave the gas firing without the tank being full of water - so as long as shutting off the gas is the first thing you do and you check that the shutoff valve has actually shut off the gas about the worst you can do is have a flood, because the water heater runs at water line pressure, not a high pressure.

I am going to assume here this is a conventional hot water tank - not a combined domestic hot water/hydronic heating system with a combined storage tank. Procedures similar with them but more connections and circulating pumps to turn off also.

Here is a link to a hundred plus prior questions with responses about typical cost of water heater replacement, and additional costs for code compliance at times -

Basic procedure, excluding units connected to solar or geothermal heat pumps or heating loops, which will have additional connections to worry about.

1) turn gas control on the water heater to OFF (the knob on the control box on the water heater that has the flex gasline coming into it and metal tubing coming out and into the firebox, knob has settings something like OFF, PILOT, ON.

2) if immediately replacing the water heater with a new one most people ignore this step or just smell or listen at the removed flex gasline to be sure the valve is actually shutting the valve off, but if leaving disconnected for an extended period of time I would do the following: first shut off the appliance gas line shutoff valve (valve on the gasline to the water heater itself, should be where the rigid gasline changes to flex tubing to reach to the water heater. Turn 90 degrees to off stop, then slightly loosen the flex line at the water heater and after the minimal pressure in the line has bled off, test with leak test bubble solution to be sure there is no gas leak getting past the shutoff valve. You will have a slight gas smell (strong right down at the open end) but if you don't hear any hiss or smell gas spreading and there is no bubbling, then valve should boe working right. This test eliminates the possibility of a slightly leaking valve building up gas while it is left disconnected, especially since they tend to be in location not frequented by the residents and are commonly close to other ignition sources like a furnace, so if not reconnecting to a new water heater right away a good idea to confirm there is no leak. Also should put a plug in the end of the flex line to prevent contamination getting into the flex line - preferably a proper threaded gasline plug - though that is a specialty item usually available only at plumbing supply sources, not ordinary box store, because of the commonly different thread.

3) turn off power at breaker or wall switch if it has external electric power - usually only if the heater has a heat pump on it

4) shut off water supply to the heater - may have a separate shutoff at the cold water pipe near to where it goes into the tank, or if not or that one is leaky may have to shut off water to entire house. In some cases a toilet tempering valve will allow backflow from the cold to the hot line so in that case, if it does not have two shutoff valves (one on each line) you may still have to shut off the main shutoff valve for the house.

5) only if water heater has been sitting a long time without use, it is a good idea to be sure the area is well ventilated before draining the tank or detaching the top piping, because it may have built up explosive hydrogen gas, or dangerous hydrogen sulfide gas. This is only a problem if the tank has been out of service for say a few weeks to month or more without water flowing through it with regular use. And if gas starts coming out, let it come out very slowly till it stops, not in one rush. And this should not be drained out at the tank if not well venitlated or is near a combustion source - you can vent it at other hot water faucets, and actually should vent at each one because the hot water lines themselves can be full of the gas.

6) drain out water from tank using the bottom drain "faucet valve", using a garden hose to drain it to a floor drain or outdoors to some point lower than the drain valve. Except for washing machine or similar special hose, make sure tank has cooled down to 100 degrees or so before draining, as some plastic hoses will be ruined by full 125-140 degree hot water - or expecially with 210 degree water if a combined heating/hot water boiler. Or you can use a bucket-by-bucket method if no low-point drain to run hose to, but bear in mind once opened the drain valves commonly they do not shut off completely on older tanks, so you may need a second container to catch the leakage while emptying your primary container. You need to open a number of hot water usage point faucets to let air into the pipe or it will drain extremely slowly or water mahy suddenly come out after you are disconnected when a vapor lock frees up in the lines - typically each bathroom and kitchen hot faucet and shower/tub faucets - in some setups with long independent run to toilets or hard-plumbed rather than tempering valve tempered water you need to flush toilets too. With the drain valve open, when you open the hot faucets you will hear a whoosh or gurgling as air goes into the line through the faucet - leave open till tank stops draining out. If it drains down with a good flow but then trails off to a trickle it may be the shutoff valve or tempering valve is allowing flow into the heater tank (and you will be able to hear water running/splashing into the tank if this is the case), so in that case you will need to shut off all water to the house. [Note - if you have shutoff valves on both lines at the top of the tank, instead of draining down the hot faucets you can just close both those valves, then after a few gallons has gone out of the tank drain (to drain down the water between the shutoff valves and the top of the tank) just break loose the fittings at the top of the tank (usually dielectric universal couplings) to let air in there instead, to hasten the tank draining. Just don't forget to reopen both valves before firing up the new water heater.

7) once tank is drained, disconnect the hot and cold pipes at the top of the tank, and cap if needed if leaking.

8) disconnect (being sure power to unit is off and tagged out so no one turns it back on) the power line to the tank, if there is one. A LOT of HVAC and plumbing contractors miswire water heater switches so only one of two hot leads is switched or so the neutral rather than the live leads are switched, so I always use a volt-ohm meter to confirm the power is off before disconnecting, and be sure to cap the bare wires with wire nuts of correct size electrical taped on to be safe in case someone turns the power back on when the wiring is disconnected

9) remove any restraining hardware - foot boltdowns, seismic restraint strap, etc

10) tank should now be ready to remove - with drain hose still attached or bucket in place, tilt to drain out remaining water in the bottom, then turn off drain valve because there will still be a few cups to quarts that may not have drained out, and those bottom dregs are usually (with a dead tank) quite rusty and make a mess of carpets and flooring if spilled. And of course don't turn tank upside down either when hauling it out. Also - there is commonly a lot of loose rust in the firebox, so if you remove the cover plate and vacuum that out it can make things neater. Some meticulous contractors slip a contractor size plastic trash bag over the bottomof the tank and tape it on if going to take the tank out through finished flooring, to prevent leaving a rusty metal trail, because as you handle it interior rust in the firebox and flue will come loose.

11) tank should now be ready (after disconnecting any drain hose) to take out of its location.

Answered 3 years ago by LCD

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