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Raypak p-r405a PRS message. tried adjusting pressure switch, no change

Water is flowing through the heater

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Clean out pump basket, backwash filter for starters. jump the pressure switch if nothing changes. if burners fire then replace the pressure switch

Posted on Mar 13, 2014


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Posted on Jan 02, 2017

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SOURCE: I have a raypak p-r405a pool heater. When i hit

Some raypaks have a remote setting. I cannot remember the exact keys to hold to change it but i think that you hold both the up and down arrows for like 10 seconds. The instructions on the particular heater that i was working with were right on the display panel, but if its not there it will be in your owners manual.

Posted on Apr 06, 2009

  • 1 Answer

SOURCE: low pressure reading on Pool Heater

I had this problem with ours last year. I replaced the water pressure switch and it began working fine. We later had a symptom that the blower would start but it would not ignite. The ignitor rod was corroded so I took it out and sanded it with some sandpaper---worked fine...until I dropped it trying to reinstall and it broke. Bought a new one and it works fine now.

Today's problem is related to the blower now.... it is always something, isn't it?!?

Posted on May 30, 2009

  • 1378 Answers

SOURCE: Heater is new, installed at grade on above ground

Adjust the switch fully in the opposite direction. If you are at 1.5 you are at the light end of the adjustment range of that switch, which can be adjusted up to 5psi. Then let it back off until it works reliably. Rarely do you need to adjust a pressure switch on an above ground pool so it should end up about in the middle of the adjustment scale.

Posted on Jul 10, 2009

  • 8404 Answers

SOURCE: My raypak heater won't relight and the pilot is on

For the heater to burn, there must be water pressure and flow - and the heater must know of it. It is not enough that you know the pump is on, the heater must know it. Check your heater's water pressure switch.

What about the filter pressure ... high filter pressure would indicate need for a backwash. dirty filters slow the water flow. If your filter normally runs at 20 PSI (when clean) it should be backwashed at 30 PSI, rule of thumb = 10 psi over 'startup pressure'.

Your heaters job is to heat the water ... think of it as a very agressive bully. The water is absolutely necessary to keep the bully in check.

Posted on May 31, 2010

  • 990 Answers

SOURCE: will pressure switch 3902 work in a raypak 255

Yes I believe so.

Posted on Jun 22, 2010

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Water heater

Most instant-on tankless water heaters require at least 10 psi of water pressure to start the heating process. The flow of water determines how hot the water will be, within the heating range. An electric 110 volts heater will increase the water temperature about 25 degrees F. A gas water heater will increase the water temperature about 45 degrees F.
Too much flow will not allow the water time to heat. Too little flow will not allow the heating system to work. Each heater must have the outflow water flow adjusted for the best heating outcomes. The best way to find the ideal flow is to turn the hot water facet on and adjust it (open or close) until the water reaches the balance of producing hot water.

Apr 25, 2016 | Water Water Heaters

1 Answer

Model h100id banging noise when turned on shuts off

VERY low water flow!
Or... No water flow.
This heater as all heaters do, need to have sufficient water flow thru them, or else they Bang like this.
This then creates a problem, for future banging - due to lime up!
The minimal water flow gets so Overheated, that it turns to steam! The steam knocks and pushes the heater around, then the Minerals will precipitate out of the water and forcefully attach to the inside walls of the heat exchanger! Which will then drastically reduce the inner diameter of the exchanger making a much smaller passageway for water to travel thru! This is a major problem to remain this way. It will then need to be dismantled and de-limed to increase the holes once more, and allow a proper water flow.

May 30, 2015 | Hayward 100,000 BTU Pool Heater H100ID1 -...

1 Answer

The heather computer indicates:Flow and does not come on

Without knowing what heater manufacturer or model, or whether this is a burner style furnace or heat pump, I would surmise a guess that you have a flow issue, a restriction in your water flow. Most water flow issues are corrected by cleaning the filter.
many people who are not in the know, or don't understand these type of things, always ask what does the filter have to do with my heater?
heaters need to have the proper amount of the water flow through them for them to fire safely and efficiently. When that water flow is reduced or restricted there is a safety sensor that senses improper water-flow, and will not allow that heater to operate. Remove the restriction, and that specific sensor that senses for proper waterflow, will allow the heater to operate.

May 19, 2015 | Pool & Spa

1 Answer

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

3 Answers

How does water flow affect Harwood H100 pool heater

if you dont have enough flow, the heater wont run. if you have a VS pump and run it at minimum speed to let heater work, the heater wont cool properly and may damage components.

Jun 27, 2014 | Hayward H Series Induced Draft Abg 100,000...

1 Answer

PRS Water pressure switch open filler was just cleaned

check copper tube to it might be plugged or pressure switch bad

Oct 03, 2012 | Raypak Pool & Spa

1 Answer

Screen has prs clean filter screen and service flashing

pressure switch is open. clean out pump basket and backwash the filter.... if you have proper water flow, jump the pressure switch....if heater fires up replace the pressure switch

Jun 11, 2011 | Raypak RP2100 DIGITAL POOL HEATER R206...

1 Answer

I installed a dhc tankless heater, but when I open only the hot water everything is ok, but when I open the cold water at the same time the heater turns off.

Hi and welcome to FixYa, I am Kelly.

What is happening is that your cold water flow is greater in volume (gals per min) than your hot water. So when you open the cold water it is mixing with the hot water inside the faucett or shower plumbing and actually reverse flowing back into the hot water heater plumbing. The reverse flow slows the water flow sensing turbine inside the heater and it is thinking that there is not any water flow. (There isn't actually due to the equalization of water pressure when you open the cold water faucett) Since this is a safety feature of the tankless heater to keep it from overheating, it shuts off.
Somewhere in the hot water plumbing there is a major restriction. It may very well be the internal plumbing of the tankless hot water heater or the flow detector design.

There are 2 ways to correct this. The easy way would be to restrict the available cold water flow. You can do this by installing another shut off valve inline with the cold water plumbing and just not open the valve all the way. You would have to adjust the setting so that the hot and cold water can be on at the same time and the hot water heater stays on. The hard way is to locate the hot water flow restriction and eliminate it.
It is possible.... if you have a flow restrictor in a shower head or a screen in a faucett areator that they are partially clogged. Clean any flow restrictors and screens then see how the hot water heater performs before you start modifying plumbing.

Thanks for choosing FixYa,

Apr 10, 2011 | Stiebel Eltron DHC-E 8 Tankless Electric...

1 Answer

Heater fires up and is hot but does not heat the water. Raypak Versa bronze

This unit must have adequate water flow and apparently needs to be checked for proper operation.

Consider the following:

The unit as manufactured is equipped with:
  • pressure switch - likely stuck in the on condition, or been has been bypassed
  • Thermostat - Needs to be checked to insure it is properly working and calibrated.
  • Hi-limit switches - need to be checked to insure they are working and not bypassed.
  • flame sensor - prevents flame from leaving the firebox and damaging control area. (if equipped)
  • Flow Governor - controls water flow through the heat exchanger to prevent over pressure.
If the pressure switch is working properly, a blockage after the heater, would create pressure, but not enough flow. Check for a closed valve or obstruction in the plumbing.

If the problem is a clogged filter, and the filter is located before the heater, then the pressure switch is NOT working correctly and needs to be replaced or adjusted to factory settings. Remove the filter cartridge and check for flow.

Bottom line is:

No flow and no pressure, - heater should not come on.
No flow, but pressure, heater would come on and overheat, tripping hi-limit.
Good flow, heater would come on and spa would heat.

Nov 26, 2010 | Raypak Hood shown but not included. A...

1 Answer

Upon start heater comes on for about 5 seconds and shuts down. Then starts again and stops again, and so on. "PRS" appears

PRS means the pressure switch is opening and shutting off the heater as you describe. Either your filter and/or inlet baskets need a good cleaning or the pressure switch in the heater is failing. Try a thorough cleaning first and then replace the pressure switch if necessary.


Oct 25, 2010 | Raypak Rp2100 Pool & Spa Heater Lonox 407k...

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