Have an Eternal (GU100, GU145, GU195) Water Heater?

Posted Oct 31, 2016

I have good and bad news

The good news is that (apart from one key issue) this is a well designed Water Heater that, if looked after will last a long time. It’s primarily constructed from stainless steel and uses good quality components.

The bad news is that Grand Hall, the company that made and sold these heaters in the US has gone bankrupt. (Apparently it’s a great heater for residential use but didn’t do well in commerical use)

Has your water pressure switch (WPS) failed?

The heater has a known design fault with the Water Pressure Switch above the heating unit. Water gradually corrodes the plastic and the switch will eventually fail, flooding the whole heater.

Eternal were aware of this issue and supplied a retrofit kit under warranty. Trouble is many plumbers didn’t inform their customers and bother to fit the kit.

So, the first thing to do is check if you’ve got the retrofit already installed:

The kit consists of a 1/8th BSP (British Standard Pipe) plug with a gasket on it that screws into the assembly (31) in place of the switch on top of the burner assembly (24). Internal cutaway of the heater

Turn off the power, remove the front of the heater, remove the screw that holds the motherboard (25), swing that out of the way and look above the burner. If you see this white plastic piece Water pressure sensor … then you still have the switch. It will fail at some point. You can see where mine sheered off when the plastic let go. Get this replaced as soon as you can. MacDonald Supply (see below) still have a few kits left, but you can really easily make one for way cheaper. All you need is the aforementioned plug: Replacement plug from any hardware store plus a jumper cable to short the switch connection and convince the CPU you still have the switch. If you’re handy with a soldering iron, you could make your own using a couple of inches of insulated wire and two 3/16 spade connectors.

Your switch just failed

Like me you maybe were unaware of any of this until the switch failed and the flood happened. If you’re frantically googling, here’s what you need to do:

First, turn off the power, then water and gas (hopefully you had an RCD and the power is already off)
With the water off you can commence mopping up of the flood.
The unit will be full of water, so remove the front to allow it to drain
Remove the single screw to swing the motherboard out of the way
Get a towel in there and start drying the inside but be delicate
It’s going to take you time to get the plug you need, so in the mean time get a big fan, point it at the heater and start to dry everything out
You’ll know it’s the WPS that has failed because it will be loose or dangling
Remove it and use needle nose pliers to remove the threaded piece that has broken off
Once you’ve dried everything out (I left the fan going a couple of days) plugged it and jumped the switch circuit you can try to restart.1.1.
With the door still open, turn on the water and check for leaks
Assuming no leaks, close everything up, turn on the power and gas
If you get no error codes, you’re good to go
However, you probably got the E27 error code…

You have the E27 error code

E27 means the mixing valve (29) didn’t initialize correctly. Boston Heating Supply (below) still have a few left but you can try to fix yourself

Mixing valve

Drain the heater (link below) and remove the two metal clips that hold the valve in place (if you have bigger hands you may want to loosen the grey air inlet tube and get it out of the way). With the valve loose, disconnect the two cables taking care not to break the tabs

With the valve out remove the two screws that hold the servo stepper motor in place. When the unit floods, the motor floods which is why you’re having issues. Gently crack the motor open by releasing the four tabs that hold everything in place. If you manage to keep all of these intact you’re a better man than I.

When I got mine open, there was water in there. I removed the three cogs, dropped the motor out and set a hair dryer on low heat on the whole thing for 1/2 hour to dry everything out.

Next I used an old toothbrush to clean all the soldered connections and make sure there were no shorts.

Once you’re comfortable it’s all dry, reassemble. Ideally you’ll have some silcon grease to put on the cogs. You’ll note that the large cog that engages with the valve has a stop built in. When you reassemble place it at one of the stops and ensure the valve is either wound fully out or in to match how you placed the cog. Otherwise you’ll get another e27 error when the motor self tests.

Once everything is in place, close the drain and air inlet valves. Open the inlet and outlet water valves. Open a faucett to allow air out of the system. Check for leaks, close up the unit and turn on gas and power.

If after reassembly you still get errors you’ll need to replace the valve. Boston has the piece, but I’m also trying to find out if you can just replace the servo. It’s a model NSAE-101 made by Nidec-Sankyo out of Japan. I’ve rung their US sales office to see if there are any retail options but haven’t had a reply yet. I’ll update this page when I find out more.

If you decide to replace..

First of all, quiz your installing plumber why they didn’t apply the retrofit kit and ensure they’re giving you a good deal.

Keep the old heater and part it out on ebay. These parts are really hard to get so you might as well make a bit of money on the side!

Useful links

Thanks to all the people who posted information to help. Questions? Ideas? Parts? Contact me on twitter @nonodename and I’ll add to this page. The Internet is a great resource for homeowners! Good luck.