Pool Heater Not firing when filter is on

[GeoffB]

This is my first post, so if you need more info please let me know.

I have an inground 25000 gallon pool, opened in Late may after wintering.

My heater (Pentair minimax) will not fire up when my Multi-flo is set to Filter. If I set it to recirculate it works. I therefore believed something was wrong with my Hayward DE filter. I took it apart and cleaned it (twice in fact) thoroughly. No improvement. I have noticed that my pressure is lower (its at 10psi) than other years, but nothing seems to take the pressure up.

I therefore now believe something is wrong with the Multi-Flo but not sure and would appreciate some advice before I take that apart.

I was advised that the DE filter Grids needed replacing to fix this problem - does that sound right? They are more than 7 years old which is how long i've had the house.

Note - I have also noticed some leaking from the waste pipe - a small amount in filter mode and a large amount in recirculate mode - does this affect the heater issue?

Any comments will be greatly appreciated.
Thanks
Geoff

 

[Red Shirt Ensign]

It could be a flow/pressure issue

I have a 2 speed pump and my heater works on low but on high the pressure valve in the heater closes.... to use it on high I would have to add an auxiliary high pressure valve which I have so far opted not to do.

 

[GeoffB]

Thanks. I agree there is a pressure issue - this pump is a new one (fitted 3 years ago) and has worked fine for that time, so I think the setup is right, just something has gone wrong somewhere causing pressure to be too low, with filter on, for the heater to start.

The heater cycles constantly trying to start, even fires, but constantly cuts out with the filter setting on the multi-flo. With the recirculate the heater starts first time, no stuttering. I'm assuming pressure is higher when the recirc is on as all the pump pressure is pushing through the system with nothing inline to reduce it.

 

[Bama Rambler]

What does the pressure gauge read on recirc?

Since it leaks a lot on recirc and your filter pressure is low on filter, it sounds like R.S.E. hit on the issue. Are you adding the correct amount of DE back to the filter? You could try partially closing the suction valve near the pump to lower the pressure/flow and see if it lights then.

 

[GeoffB]

Pressure gauge reads low to zero on recirc.

It says 7.5lbs of DE so that's what i've been adding, always seemed to work for last few years.

I think i've tried it with one return value closed - is that what you mean to change the pressure? I'll try it again.

If it does work, any idea what would be causing this?

BTW - I meant its a Hayward Vari-Flo not multi-flo as I had said.

Thanks for the advice.

 

[GeoffB]

I closed one of the valves from the pool to see if it changed the pressure and caused the heater to fire. No difference, on filter the heater won't fire, on recirc it starts.

I'm thinking of replacing the spider gasket on the variflow (especially since i'm getting a leak) and views if that will help the pressure issue?

Thanks

 

[Bama Rambler]

That points to it being a flow issue and not a high pressure issue. Is there a flow switch in the system?

 

[GeoffB]

No flow switch that I know of.

Interestingly, i just went away for 4 days, came back, vacuumed pool (some debris due to storms), pressure in DE went upto 12, heater now working. Not sure what will happen when I backwash, but i'm going to leave it running for a while to see what happens.

 

[Bama Rambler]

This is very interesting. If the filter pressure went up then the pressure and flow that the heater sees went down and now it works. Maybe it's a dual pressure switch that senses high or low pressure and now you're in the normal range. Could be as simple as the pressure switch going bad.