jdenmark

Member
Dec 24, 2020
6
Massachusetts
Hi all,
Novice repair person here. My Hayward spa heater (installed 2018) is not heating the water and is displaying this LO code. I have read every troubleshooting guide and watched every video I could find. My diagnostics included:
1. Cleaned the filters, even ran the pump without the filters - still LO
2. Checked wires at pressure switch for continuity - still LO
3. Checked heater for mouse damage - still LO
4. Switched out the pressure gauge with the one used on my pool filter - still LO
5. Adjusted the pressure switch for easier contact - still LO

I have ordered a new pressure switch and new pressure gauge, and will try to switch those out. I cannot get a hayward repair person to my region and no one local has experience with hayward. I'm frustrated and see lots of freezing nights on the horizon.... Thanks for any thoughts.
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,185
FL
Hi all,
Novice repair person here. My Hayward spa heater (installed 2018) is not heating the water and is displaying this LO code. I have read every troubleshooting guide and watched every video I could find. My diagnostics included:
1. Cleaned the filters, even ran the pump without the filters - still LO
2. Checked wires at pressure switch for continuity - still LO
3. Checked heater for mouse damage - still LO
4. Switched out the pressure gauge with the one used on my pool filter - still LO
5. Adjusted the pressure switch for easier contact - still LO

I have ordered a new pressure switch and new pressure gauge, and will try to switch those out. I cannot get a hayward repair person to my region and no one local has experience with hayward. I'm frustrated and see lots of freezing nights on the horizon.... Thanks for any thoughts.
Did you jump out / bypass the pressure switch to see if the "LO" error went away?

What "pressure gauge" on the heater did you switch out???

What model is this heater?
 

jdenmark

Member
Dec 24, 2020
6
Massachusetts
Did you jump out / bypass the pressure switch to see if the "LO" error went away?

What "pressure gauge" on the heater did you switch out???

What model is this heater?
Thanks for suggesting this.
I just switched out the pressure switch, but the new one did not fix the problem, so I think I can rule out that device. The pressure gauge that I switched is the one on the top of the water filter. It wasn't zero'ing out when the pump was off, so I thought maybe something was wrong with the pressure coming from the filter.

I've never jumped or bypassed anything, so I'm a little nervous to do that on my own. I do have an electrician coming over in a few days, so I'd wait for the professional to do that.
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,185
FL
If the new pressure switch didn't resolve it then jumping it out will have no change on the error as well. An electrician most likely won't be of much help either. They don't usually don't work on gas pool heaters and most likely can only confirm that you have power to the unit which you already know.

There are also two temp limit switches on the side of the unit that if bad can cause an "LO" code as well. Measure for continuity across them and if open, replace them. Of course you can also temporarily bypass them and see if the error goes away.

What model of heater do you have?
 

jdenmark

Member
Dec 24, 2020
6
Massachusetts
If the new pressure switch didn't resolve it then jumping it out will have no change on the error as well. An electrician most likely won't be of much help either. They don't usually don't work on gas pool heaters and most likely can only confirm that you have power to the unit which you already know.

There are also two temp limit switches on the side of the unit that if bad can cause an "LO" code as well. Measure for continuity across them and if open, replace them. Of course you can also temporarily bypass them and see if the error goes away.

What model of heater do you have?
Thank you, Paul! The heater is an H150. It is installed inside a pool shed and is vented through the roof.
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,185
FL
Thank you, Paul! The heater is an H150. It is installed inside a pool shed and is vented through the roof.
Ah, it's inside a shed. Then you need to check the vent to make sure it's no blocked or restricted. Also, check the vent pressure switch and hose to make sure they are good as well. Disconnect the vent pressure switch and check for continuity as well. If it is open, replace it.

Having a unit inside changes the normal routine for checking certain things especially for the "LO" code.
 

jdenmark

Member
Dec 24, 2020
6
Massachusetts
Ah, it's inside a shed. Then you need to check the vent to make sure it's no blocked or restricted. Also, check the vent pressure switch and hose to make sure they are good as well. Disconnect the vent pressure switch and check for continuity as well. If it is open, replace it.

Having a unit inside changes the normal routine for checking certain things especially for the "LO" code.
I just opened the vent and used a shop vac to clean out. Mostly just dead insects. I also got the shop vac into every place I could. Definitely some mouse droppings around the heater. I will have the electrician check for continuity on the pressure switch next.
 

jdenmark

Member
Dec 24, 2020
6
Massachusetts
Ah, it's inside a shed. Then you need to check the vent to make sure it's no blocked or restricted. Also, check the vent pressure switch and hose to make sure they are good as well. Disconnect the vent pressure switch and check for continuity as well. If it is open, replace it.

Having a unit inside changes the normal routine for checking certain things especially for the "LO" code.
Well, the electrician came out this morning and everything checked out. Water pressure switch, temperature limit switch, vent pressure switch and vacuum switch all seemed to be ok. We let it try to cycle through startup multiple times. One cycle (out of about 20) the heater almost fired. Not sure if that might indicate anything...
 
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