Question about Hayward H-series Electronic Gas Pool Heater H400

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Why is my flow low through my heater - Hayward H-series Electronic Gas Pool Heater H400

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Pump basket may need to be cleaned out...sand filter may need to be backwashed....cartridge filter may need to be cleaned out

Posted on May 06, 2014


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SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

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Fl0 code

Flo ? for Flow Error?

That would for any number of reasons that the Flow Switch is not sensing enough water flow to trip the sensor/pressure switch or actual true water flow switch.

Heater will not run or heat, if there is not enough water flowing!
The heater will sense this. So, whatever will restrict or stop sufficient water flow is the problem.
  • Dirty filter
  • Closed valves
  • Not enough water in tub or pool - low water level
  • Clogged pump impeller
  • Clogged baskets:
    • at pump or at skimmers
  • Clog / stopped up plumbing line
And finally, you may have a bad flow switch/sensor

Sep 06, 2014 | Jandy Pool & Spa

2 Answers

What does lo mean on my h250 hayward pool heater

LO standss for limit open. the most common cause is lack of adequate water flow through heater. other causes are high temp limits.

Jun 10, 2014 | Hayward H Series Pool & Spa Heater 400k...

1 Answer

Rheem 22v50f1

Backflow preventer is not part of water heater:

Water heater might have heat trap nipples that get clogged... but other issues have to be eliminated:

Gene h

Mar 27, 2014 | Water Heaters

1 Answer

2002 toyota celica heater does not work

The thermostat should only restrict flow to the radiator.
If the heater system is working correctly, you should get flow from one of the heater hoses at all times.
Its possible you have air in the cooling system.

Jan 06, 2013 | 2002 Toyota Celica

1 Answer

Need Heater Hose orientation for 1970 Ford Mustang 351 Cleveland bought in pieces

Sorry I can't give you a definite answer but as a general rule the coolant control valve will control the flow, supply or hot heater pipe that originates at the cylinder head or near the top of the engine.

Even though the heater matrix ******* are side by side they will usually be routed in the internal construction of the matrix to a high and a low position. It often makes little difference which way around the flow and return are fitted but one school of thought is to connect the flow to the top and the thermosyphon tendency will aid the flow and the other school of thought suggests if the flow is low to high any tendency to airlock will be reduced.

Jul 23, 2017 |

1 Answer

No heat in car

Check low antifreeze level--- Replace thermostat-- heater coil plugged, check for flow through heater coil, heater coil outside plugged no air flow replace air filter in dash and clean outside of heater coil if you have very low air movement to defrosters--- try this last thing first --- cheapest things first ,

Oct 08, 2012 | 1998 Ford Taurus

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Hayward spa heater about 5 years old, when we turned it on for the first time in probably a year as soon as the water heater came on it started making a loud clanging sound

Thank you for posting your question here on

For starters you will need to proceed carefully...the noise you hear is water beginning to boil within the heat exchanger. The pressure that results can cause the unit to rupture or worse, blow. DO NOT ALLOW THE HEATER TO OPERATE IN THIS CONDITION FOR MORE THAN A MOMENT OR TWO as you attempt to repair it.

Water boils in a heater due to low flow, allowing the water to get too hot as it passes thru, or a faulty part or parts within the unit. We'll start with parts:

The bypass valve inside the header may be the issue if it is stuck closed. You will also want to inspect the thermostatic control valve in the header (if one is present) and inspect the overall condition of the heat exchanger. It is likely aggressive water has damaged some or all of these parts causing the banging noise you hear.

If the heater checks out then flow is the likely cause. It is possible there is an issue with the pump and/or filter not getting enough flow thru the heater. Check the overall system flow. If it is reduced too low the water inside the heater gets too hot and begins to boil causing the noise you here. Speeding the flow back up will eliminate the issue. Check all the trap baskets and the filter for debris and clean up what you find; backwash a sand filter or clean a cartridge or DE unit. If your pressure gauge is broke replace it and check system pressure. If it is low again that is a sign of a flow problem. If flow is low and all these items check out open up the pump and inspect the impeller for clogged vanes or a blocked inlet eye.

If this answer does not fix your problem, please comment with additional details prior to rating the answer. Positive feedback is appreciated once your problem is solved!

Mar 14, 2011 | Hayward H Series Pool & Spa Heater 400k...

1 Answer

I receive Lo H20 message at an air energy heat pump. Probable problems?

This is pretty common for LOW FLOW through the heater. Most of the time, homeowners turn the bypass the water away from the heater and this reduces the amount of water flowing through the heater. Check the bypass to ensure that you have enough water flowing through the heater.
There is nothing else that will throw this code unless the flow sensor is bad altogether.
Once you have inspected your bypass, and the code reappears, you will need to have the heater inspected and possibly change out the flow sensor.

Dec 07, 2010 | Jandy Air Energy Heat Pump - 100,000 Btus

1 Answer

My kitchen facet will not activate the hot water buner now and it takes two hot water facets in the bathroom to activate hot water. Is there a maintenance pronlem I need to do? Where are instructions how...

There is a minimum water flow required to operate your Bosch tank-less water heater. It is around .75 gallons a minute. There are three things you can do to help the flow.
1.Turning the temperature down will help increase the flow.
2. Installing higher flow aerators on your faucets.
3. Clean the Bosch tank less water heater.
You are not alone in having this issue. The most common problems are low flow faucet aerators and low flow shower heads.

Aug 31, 2010 | Bosch Water Heaters

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