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Pressure-Balancing Is Not Thermostatic

These two get used as though they were the same product. They are not, they solve different problems, and knowing which you have explains most of what your shower does.

At a glance

ASSE 1016 covers three types: Type P pressure-balancing, Type T thermostatic, and Type T/P. Most American showers are Type P, which holds the balance between hot and cold when pressure changes and has no idea how hot the hot water arriving at it is.

Source: ASSE International, Adjustment of Automatic Compensating Valves to Prevent Potential Scald Hazards.

ShowerValve is a referral service, not a contractor. We connect homeowners with independent contractors. Contractors are required to hold whatever credential their state or municipality demands, and valve work opening a wall is often a permitted alteration — ask to see the permit. We carry out no work, we sell no valves, we do not set prices, and we never charge homeowners anything — the contractors in our network pay us when we route them a call. The maximum water temperature is set by your local code, not by this website.

The three types in the standard

ASSE 1016 covers Type P, a pressure-balancing compensating valve; Type T, a thermostatic compensating valve; and Type T/P, a combination of both.

Both look identical from the bathroom. A Type P holds the balance between what arrives; only a Type T knows how hot the water leaving it is.

Most showers in American houses are Type P. It is the common product, it costs less to make, and for the problem it was designed for it works well.

Source: ASSE International, Adjustment of Automatic Compensating Valves to Prevent Potential Scald Hazards.

What a Type P actually does

It watches the balance between the hot and cold supplies and holds it when one of them changes. Somebody flushes a toilet, cold pressure drops, and the valve cuts the hot proportionally so the mix does not swing.

It is responding to pressure, not to temperature. It has no idea how hot the hot water is. If the water arriving on the hot side gets hotter, a Type P holds the same balance and delivers a hotter shower.

What a Type T does instead

A thermostatic valve measures the outlet temperature and moves to keep it where it was set, regardless of what the supplies are doing. It is answering the question people think their shower is answering.

It costs more, and it is the reason some showers hold a temperature through anything while others do not.

Which explains which complaint

The shower goes cold or hot for a few seconds when an appliance runs, then recovers. That is a pressure event, and it is what a Type P is for — if it is not recovering, the valve is worth looking at.

The shower is fine at the start and creeps hotter, or is different in the morning from the evening. That is a temperature change on the supply, and a Type P was never going to correct it. Which is which, in more detail.

Why it matters before a replacement

Because “replace the valve” can mean like-for-like or can mean changing type, and the second is a different job with a different outcome. Ask which is being quoted. What replacement actually involves is worth reading first.

Ask whether it is the cartridge or the body.One is work through the trim, the other opens a wall, and the answer changes everything about the job. We will route you to somebody who covers your area, worked out from your ZIP code, and you are never charged. And if trouble elsewhere in the house needs attention, bring it up when you call.

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