I had to rerun a pool pump and pool light circuit for a pool at a home. It also has a gas heater which needs 120v to it. Can I tie that into the line side if the GFI (light) circuit. I don't think its code to use half the 240v pool pump ckt, 120 v side, with the GFI line in for neutral. Is it? So I would be sharing the 120v side of the pool pump circuit for the control panel on the gas pool heater, doesn't draw much, but couldn't find it in the code book. Line side of the pool light circuit would probably be ok.

If you had a neutral it could be on that circuit (pump),(210.4(C) ex2) in fact I think the gas heater instructions do say you should be on the pump circuit. The problem is you should also be sure the pump runs several minutes after the heat turns off so if you have a timer you will need a way to keep the pump going.

Most pool heaters are 120/240 volts. The pool heater can be connected to the load side of the pump time clock.

The only problem with using the pool time clock is the heater instructions say you need to run the pump for up to 15 minutes after the heat goes off. Whenever the heater is on in my pool there is a parallel circuit that holds the pump on and maintains that for 10-15 extra minutes (a fairly simple circuit discharging a big capacitor across a darlington, picking a relay)

Greg,
That's why there is a fireman's switch in the time clock to shut the heater off 20 minutes before the pump.

So, the "fire mans switch is auto?
I've done pool heat pumps but not boilers.
On the heat pumps there is an option for a relay/contactor that goes in paralel with the load (pump), to maintain temp.
Side note: They don't need GFCI,just the bond(in MA.) I thought that strange.

I would think that with the boiler the override and timeing relay would be standard if this crucial.

However I've done some looking at diagrams and I don't see that. Strange.

It is not a relay, it's a micro switch that is connected to the clock mechanism that shuts the lovo side of the heater off 20 minutes before the pump.

Yup The "fireman switch" just opens on the 24v to the whole unit. Since I wasn't sure what my timer was going to end up being I built the delay off on the pump separately, about as fail proof as I could make it. The 15 minutes is really overkill. After the gas goes off the water temp drops pretty fast. In a minute it is close to pool temp.

"The 15 minutes is really overkill. After the gas goes off the water temp drops pretty fast. In a minute it is close to pool temp."

I agree.