Leaking T&P relief valveWhen a temperature and pressure  (T&P) relief valve at a water heater leaks, it's unremarkably a elementary fix; just replace the valve.   These valves toll less than $xv, and replacing the valve is a very bones job - but drain some water out of the water heater, remove the discharge tube, and replace the valve.  No big bargain.

Unless it starts leaking again.

If a recently replaced T&P relief valve starts leaking again, it probably means that the relief valve is only doing it's chore; it relieving backlog pressure in the h2o heater.  When this happens, the prepare gets a little bit more involved.  I'll explain.

When a water heater heats up the h2o in the tank, the water expands.  When this happens, the water typically ends upwards expanding back out the cold h2o inlet, all the way back to the h2o supply coming in to the firm.  The municipal water supply for the house acts as a gigantic expansion tank... and nobody notices.  This is illustrated in the diagram beneath.

Natural expansion

What would happen if a i-way valve, or bank check valve, was installed on the water supply piping for the house?  The water wouldn't have anywhere to go.  As the water heater heats the water, it expands, which builds upwardly pressure in what is at present substantially a airtight system.  When the force per unit area builds upwards enough, the T&P relief valve on the water heater just does it's job and relieves the excess pressure past leaking a petty water.

Pressure regulator prevents expansion

In Minnesota it'due south rare for a check valve to be installed on the water supply line for the house, but it's fairly mutual to take a pressure regulator installed.  When the pressure from the water supply coming in to a house is besides high, a pressure regulator needs to be installed on the water primary, to prevent impairment to the plumbing components in the house.  The problem that these regulators can create is that they volition deed as a check valve; they'll allow h2o in to the home, merely they won't permit water back out.  This creates what is chosen a 'closed system'.

When this happens, the T&P relief valve for the water heater tin leak.  This doesn't happen every time a pressure reducing valve is installed, simply there may be other problems that show up in the house, such as the toilet fill up valves randomly re-filling toilets, or faucets chronically dripping.

The FixWhen a closed arrangement exists on the water distribution piping in a dwelling house, an expansion tank needs to be installed somewhere on the plumbing organisation.  This is a fairly simple and straightforward fix; an expansion tank will give the water somewhere to go when information technology expands, and the T&P relief valve on the water heater will stop causing issues.

Expansion tank installed

This rule likewise applies to hot water heating systems; when a boiler heats the water in a hydronic heating organization, the expansion tank allows for the h2o to expand without the pressure relief valve leaking.  If the pressure relief valve on a banality system chronically leaks, fifty-fifty after replacement, it probably means there is a problem with the expansion tank.

Reuben Saltzman, Structure Tech Dwelling Inspections - Email - Maple Grove Home Inspector