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AGE of WATER HEATERS
ALTERNATIVE HOT WATER SOURCES
ANODES & DIP TUBES on WATER HEATERS
ANTI SCALD VALVES
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
AQUASTAT CONTROL Functions
BACKDRAFTING HEATING EQUIPMENT
BACKFLOW PREVENTER, HEATER WATER FEEDER
CARBON MONOXIDE - CO
CHECK VALVES, WATER SUPPLY
CLOGGED SUPPLY PIPING
CROSS CONNECTIONS, PLUMBING
DEBRIS in WATER SUPPLY, Water Heater
DRAIN a WATER HEATER TANK
ELECTRIC WATER HEATERS
FLOODED WATER HEATER REPAIR
FREEZE-PROOF A BUILDING
GALVANIC SCALE & METAL CORROSION
GAS BURNER FLAME & NOISE DEFECTS
GAS FIRED WATER HEATERS
GAS PIPING, VALVES, CONTROLS
HEATING COST SAVINGS METHODS
HOT WATER EXPANSION TANKS
HOT WATER SUPPLY
HOT WATER IMPROVEMENTS
HOT WATER DELIVERY SPEED UP
HOT WATER EFFICIENCY IMPROVEMENT
HOT WATER PRESSURE EXPANSION RATE
HOT WATER PRESSURE IMPROVEMENT
HOT WATER PRESSURE LOSS
HOT WATER PROBLEM DIAGNOSIS
HOT WATER QUANTITY IMPROVEMENT
HYDROGEN SULFIDE GAS
INDIRECT FIRED WATER HEATERS
MANUALS & PARTS GUIDES - HVAC
MIXING / ANTI-SCALD VALVES
NO HEAT - NO HOT WATER: HEATER DIAGNOSIS
NOISE, WATER HEATER
ODORS IN WATER
PIPING IN buildings, Clogs Leaks Types
RELIEF VALVE LEAKS
RELIEF VALVE, WATER HEATER
SCALE REMOVAL, WATER HEATERS
SEWER GAS ODORS
SOLAR HOT WATER HEATERS
TANKLESS WATER HEATERS
THERMAL EXPANSION of HOT WATER
THERMOSTATS, WATER HEATER
TIMERS for ELECTRIC WATER HEATERS
WATER HEATER ALTERNATIVES
WATER HEATER ANODES, DIP TUBES
WATER HEATER AIR INLET
WATER HEATER DEBRIS FLUSH
WATER HEATER DRAIN PROCEDURE
WATER HEATER EFFICIENCY
WATER HEATER FLUSH PROCEDURE
WATER HEATER NOISES
WATER HEATER PROBLEM DIAGNOSIS
WATER HEATER COMPARISONS, PROPERTIES
WATER HEATER SCALE
WATER HEATER SAFETY
WATER HEATERS for HOME HEATING USE?
WATER ODORS, CAUSE CURE
WATER PIPES, Clogs Leaks Types
WATER PRESSURE TOO HIGH: DANGERS
WATER PRESSURE LOSS DIAGNOSIS & REPAIR
WATER QUANTITY IMPROVEMENT
WATER SOFTENERS & CONDITIONERS
WINTERIZE A BUILDING
Hot water pressure problem diagnosis & cures: this article describes the steps in diagnosing & correcting bad hot water pressure. If cold water pressure is acceptable but hot water flow rate or pressure are weak you'll see what to do in this article.
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Poor hot water flow but good cold water flow at one or more plumbing fixtures usually diagnoses either a blockage at the water heating equipment itself or mineral clogging in the water heating system piping.
Heat causes mineral precipitation out of hot flowing water faster than out of cold water, that’s why often mineral clogs appear on hot water components of a plumbing supply system first. For example in the electric demand water heater shown at left, if incoming water is high in mineral content, expect scale formation inside the heater that will eventually slow flow through the device.
[Click to enlarge any image]
When only hot water supply, pressure, or flow are poor while cold water pressure is good, then we take a different approach, focusing on hot water supply equipment, piping & controls.
Note: Building water pressure that is poor at all fixtures at both hot and cold water taps may be due to clogged building cold water supply piping. Other links at the end of this article provide guides for diagnosis and repair of other causes of bad water pressure throughout a building.
Start diagnosing weak hot water flow & pressure right at the water heater or cylinder
Diagnosing poor hot water pressure & flow when cold water pressure and flow are acceptable begins at the water heating device itself.
1. check the cold water supply
Make sure that the cold water supply into your water heating appliance is adequate and not blocked. Usually if you can confirm good cold water flow at a drain or fixture valve very close to the water heater you've answered this question, but don't rule out a partly closed or obstructed control valve or pipe connection, tee or elbow close to the water heater itself.
If your check shows that cold water supply flow & pressure are poor, start diagnosis at CLOGGED SUPPLY PIPES, REPAIR
2. check the hot water heating appliance
Select the link below that describes your building's method of producing hot water: the calorifier, hot water cylinder, geyser, or water heater.
3. check hot water piping between the heating appliance and the plumbing fixture
4. check the plumbing fixtures
If only hot water pressure and flow are poor, and if your hot water is made with a tankless coil see these articles for diagnosing and improving hot water from a tankless coil:
Acid flush of the tankless coil: If hot water is made by a tankless coil, often the coil itself has become blocked with minerals. A blocked tankless coil can be cleaned by flushing it with acid.
But beware, acid flushing a coil is not a permanent repair, and some plumbers will tell you that the acid-etched pipe surface inside the tankless coil will clog more rapidly than before.
Install a water softener: If you find a pile of tankless coils like those in this photo during a building inspection you might suspect that this building has had a history of repeated clogging of tankless coils used for domestic hot water. After the tankless coil was flushed with acid, the building owner would have been better off installing a water softener to protect against subsequent mineral clogging of the tankless coil interior.
How else can we Improve the Hot Water Volume & Quantity When Water is Heated by a Tankless Coil?
See HOT WATER IMPROVEMENT for a detailed guide to improving hot water quantity and flow when a tankless coil is installed as well as using other methods of hot water heating
See MIXING / ANTI-SCALD VALVES for details about mixing valves on boilers and tankless coil systems and for an explanation of how an anti-scald or tempering valve can increase the volume of hot water available from a tankless coil hot water system.
We discuss tankless coils in detail at Guide to Tankless Coils on Heating Boilers.
Building Hot Water Pipe De-Scaling: Use of acid flushing to clear tankless coils or building water piping
Clogged hot water piping itself can also be due to minerals and may appear worse than on the cold water piping. Some plumbers offer a service of acid flushing the entire hot (or hot and cold) water piping system. If you see minerals building up on fixtures such as the extreme case in our photo at left, you definitely need a water softener.
We discuss the procedure tankless-coil lime-removal by acid-flush procedure in detail at CLOGGED TANKLESS COIL & HOT WATER FLOW.
But any of these acid flush or component replacement “fixes” for mineral-clogged hot water piping or heaters are temporary at best. A better and long lasting repair is to have the water tested for hardness (confirming that there is a mineral problem) and then the installation of a water softener system.
But don’t kid yourself. While installing a water softener will protect water piping from further mineral clogging, it will not un-clog or remove caked-on minerals that are already clogging the system.
For a complete list of articles on diagnosing hot water problems see
What to Do to Improve Hot Water Pressure Where Long Sections of Hot Water Piping are Clogged or Hot Water Pipes are Too-Small in Diameter
The following hot water piping improvement advice is adapted from CLOGGED SUPPLY PIPES, REPAIR .
Local water piping clogs can cause bad water pressure in entire sections of hot, cold, or both hot and cold water supply pipes and fixtures in a building.
Local hot water supply pipe clogs due to minerals in the water may clog entire lengths of piping so badly that the only repair is replacement of the water supply pipes.
In other cases a plumber may offer to try an acid-wash to de-scale the hot water piping interior.
Certainly if we find that this is what’s needed, there are two approaches that can protect the investment in improved water flow.
These can both be done or you may choose just one of them.
We took this second approach on a building where we found that the hot water line clogged with a combination of minerals and iron.
On cutting open the old hot water supply pipe we saw that its interior was blocked to a mere pinhole of remaining water passage.
But the cold water line was basically clear. So we replaced the hot water line, including straight runs and all elbows, with a ¾” copper pipe. The repair has continued to function well for nearly 30 years.
Water Pipe Clog Diagnosis, Cleanout, Repair Artivcles
Contact us know if you have other questions or repair ideas or if this material leaves you with a question or suggestion.
Continue reading at HOT WATER QUANTITY IMPROVEMENT or select a topic from the More Reading links shown below.
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