I have a raypak heater. when i turn it on it heats up and soon after it starts to shake and it shows error code HL1. i suspect its overheating but not sure why.

This issue sounds tricky. I recommend you callthe Raypak technical support at 800-947-2975 or 800-627-2975 and they should beable to help you figure this issue out.

I hope this helps.

Possibilities:

1-low water flow (this heater needs 45 GPM minimum to operate safely
2-blocked heat exchanger (flush exchanger through drain ports)
3-Unitherm Governor (already replaced)
4- Bad bypass assembley or bypass spring (these bypass assembleys do fail occasionally)

Id start with making sure the water flow is proper, and if that checks out ok, id replace the bypass spring and assembley.

Note: when examining bypass assembley, if spring is worn or missing, start with this only as its cheapest)

high limit 135 error

You didn't indicate what model heater you have, but here are some of the fault codes you might see. Could it have been GVO? You can download a manual for your exact model at www.raypak.com
BD1 Board failure
EEP Microprocessor error
FAN Blower pressure failure
FFL Flame sensing when pilot and gas
valves are closed
GVC Gas valve closed
GVO Gas valve open
HL1 High limit switch #1 open
HL2 High limit switch #2 open
IGN Ignition failure
ILO Ignition lockout - Propane units only
PRS Water pressure switch open
ROL Heat roll-out safety switch open
SNS Sensor failure, Water temp. below 36°F
or above 110°F
VNT Vent switch open

I think the codes mean:

• PRS Pressure switch
• HL1 High limit 1
• CFH Call for heat

If this was my heater, I'd ring up for a service call.

Check the bypass in the header for damage. HL1 along with the banging/popping is too low of water flow through the heater and the water is getting to hot.

the heater is plump correctly?if yes assembly valve need replacement, if you by pass before dirt may be inside.