Hayward H250 16 years old……. Solid service light- blinking LO error…..

LO is a limit string so it checks the loop of multiple sensors before firing. One of those hls must of been open upon LO test that’s probably why it fired. If the pressure switch engages microswitch, I would jump or test each hls individually one of them is open. For future reference don’t cut the wire just use the quick disconnects and bridge with a small piece of wire.

We’ll I have been wiring patch-bays in recording studios since the 80’s - so cutting wire and rewriting is kinda my default
 
They are high limit switches, they open if the water reaches 135f, 160f. They are safety features so if the water after the heat exchanger gets too hot it shuts the system down. One of them presumably was bad that’s why it fired up when you jumped them. You have to figure out which one is bad by jumping them individually or replacing both. The pressure switch could be good if the piston hits the microswitch and the microswitch is working properly a simply continuity test would work. Jumping any safety switch should be done for testing purposes only and the jumper should be removed after.
 
Those are the hi-limit sensors that keep one from getting scalded if there is a malfunction of the water management system. Safety systems should NEVER be bypassed. When all systems are good, a pool heater is very safe. If even one is bypassed they are incredibly dangerous. You don't want to see the harm that can result from this practice.
 
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They are high limit switches, they open if the water reaches 135f, 160f. They are safety features so if the water after the heat exchanger gets too hot it shuts the system down. One of them presumably was bad that’s why it fired up when you jumped them. You have to figure out which one is bad by jumping them individually or replacing both. The pressure switch could be good if the piston hits the microswitch and the microswitch is working properly a simply continuity test would work. Jumping any safety switch should be done for testing purposes only and the jumper should be removed after.

I know the pressure switch is shot because the posts on one contact are disconnected- the hi limit switches may also be shot - I just ordered replacement sensors - and am gonna replace them all -

Cheaper than a new unit !!!

Thanx again for the insight
 
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I know the pressure switch is shot because the posts on one contact are disconnected- the hi limit switches may also be shot - I just ordered replacement sensors - and am gonna replace them all -

Cheaper than a new unit !!!

Thanx again for the insight

I had a new one in the basket on sat - now thanks to some insights - I have sensors on order and the entire season to get them installed- I don’t use the heater during summer - pool is 87 degrees today 😳😳😳
 
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