Spa heater issues

[bbuck79]

Pentair Mastertemp 125

Been running a month or 2 with zero issues when suddenly it stopped working with a service heater light.
Reset and listen to the ignition sequence and notice that after the burner ignites for several seconds, something switches and the whole system whines and groans.
It is not a blower obstruction, I've pulled this apart and verified, also the blower comes up first with no noticeable issues it's after the ignition.
I've noticed that if the system is cold, say 70F it will start and make noise but the noise quickly subside.
The noise starts to return around the 90F mark.

I've been talking to Pentair but they are limited help. Anyone know what I should be looking into? Hopefully someone can help. I also have a video of the heater running when the issue occurs.

https://youtu.be/rNzjS8pxioU

In the video the system has already fired and about 5 seconds in you can hear it whine as something is engaged or a valve is opened or something.

Any help would be appreciated.

[Denniswiseman]

Is there a good water flow through the unit
Is the filter clean
It could be a dodgy pressure switch
You can also temporarily bypass the pressure switch by using a jumper wire to make good contact with both terminals on the switch. If the switch is the problem, bypassing it should allow your heater to start running.

[bbuck79]

Water flow is good, first thing the unit does before firing up is check flow sensors, if the flow is too low it won't even fire and give a service light.
Filter is likewise good and clean
Pressure switch was the first thing .... I think I know what you are talking about to bypass but I might snap a picture and post just to be sure.

Thanks!

[bbuck79]

I also tested bypassing the pressure switch as suggested and it made no difference.