How do I stop hot water coming out of the overflow pipe. For a week the heater was off. Upon turning the water heater on and after the water was heated it began to run out of the overflow pipe.

SOURCE: hot water coming out of overflow pipe on my vulcan everhot water

Assuming you are talking about the temperatur/pressure relief valve, it is stuck open.

1. Turn off gas or electric to water heater
2. Close water supply to water heater
3. open hot water faucet on nearest fixture to depressurize hot water system.
4. close tpr valve (you may have to push in on the center spine. It may be resistant to closing from sediment. If so, opening and closing several times may solve that issue.

Once you get the tpr valve closed, close the faucet and open the supply valve. If the tpr stays closed, go ahead and turn on the gas/electric and re-light pilot and turn on control etc.

If the TPR blows again, you will need to replace it. YOu can buy a new one at any plumbing supply store. Shut down the heater again, drain a bit of water out using the valve on the bottom of the tank. there is probably copper pipe connected to the TPR valve which you may have to cut or maybe can just unscrew. The TPR threads out of the tank, install the new valve (make sure to use pipe dope or teflon tape.

SOURCE: Very Hot water coming out of overflow pipe

Is your boiler heating your domestic hot water if so i would turn water off to water maker and see if your boiler pressure stays down below 20 psi. If so water maker is bad. The other thing that could cause this problem would be the boiler pump is out.

SOURCE: Tankless water heater pilot light will not stay on

It is most likely the water valve stuck open, telling the controls to heat water, that it thinks is flowing through it, but without actual flow it overheats. Depending on how comfortable you are with taking it apart yourself, you could open the valve to see if it just needs cleaned out, or if you have a ruptured diaphragm or some other cause.

SOURCE: Worcester combi boiler losing pressure & water through o/flow

having the same problem and its a new bolier. thanks , adriano.

SOURCE: Paloma PTG 74PV N1 Tankless Water Heater - stops heating

Most likely problem is the remote control not the main board. A safe temporary fix is to unplug the heater from the 110 volt outlet, remove the two low voltage wires from the remote control and use a small wire nut to connect the two conductors together. Plug the heater back into the 110 outlet and the heater should work just fine. The default water temperature is about 118 degrees at the heater. Replace the remote control ASAP.