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Rick, Construction Supervisor
Category: Plumbing
Satisfied Customers: 21386
Experience:  Licensed Master plumber with 40+ yrs. experience.
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My name is ***** *****. When I flush my downstairs toilet,

Customer Question

Customer: Hi my name is ***** *****. When I flush my downstairs toilet, my hot water heater will make a knocking sound. It doesn't do it all the time.
JA: Thanks. Can you give me any more details about your issue?
Customer: It sounds like a gargling/thumping noise. It just recently started and only when the 1st floor toilet is flushed. The 2nd floor toilet connects off the same water lines, just 6ft before the 1st floor toilet. The water heater is about 6years old
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Submitted: 1 year ago.
Category: Plumbing
Expert:  Rick replied 1 year ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

What is your concern?

Customer: replied 1 year ago.
As I said before, when I flush my 1st floor toilet, the hot water heater will make a knocking (loud gurgling) sound. It doesn't do it all the time. Perhaps when the hot water heater is refilling the same time the toilet is flushed.I have verified that the toilet is using cold water. When I shut off the cold water valve, the toilet gets cut off. I DID recently remove the 1st floor toilet when redoing the bathroom floors. That could be around the same time the water heater started making noise. I read that the hot water heater could be "sucking" water due to lack of pressure.
Expert:  Rick replied 1 year ago.

The water heater never drains unless you shut the valve on the cold water line off and hook a hose onto the bottom of the tank. It's always full of water under pressure so flushing the toilet would have no impact on the water heater. I suspect the noise is coincidental to flushing the toilet not caused by flushing the toilet. The type of noise you describe is often happens when the burner or heating element comes on. Its caused by mineral build up or sediment build up in the bottom of the tank.

Customer: replied 1 year ago.
the solution would be to... drain the tank?
Expert:  Rick replied 1 year ago.

You can try flushing the tank. Here are instructions:
Turn the water off to the tank and turn the gas valve to pilot. If this is an electric heater turn off the power to the heater. Then hook a hose onto the drain faucet at the base of the tank and open the drain. If no water comes out turn the water back on to the tank to get it going then shut it off again. Next open a hot water (only) sink faucet to let some air into the tank so it can drain. Once the tank is drained close the sink faucet you opened but leave the hose attached and the drain faucet open and turn the water back on full blast to the tank. Let it run for 5 to 10 minutes then close the drain and let the tank fill. Next open a hot water faucet and let it run until the air stops spitting then turn the gas (or power) back on

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