You know what isn’t fun? Taking an ice-cold shower in the middle of November.

You know what also isn’t fun? Telling your husband you screwed up the pressure in the hot water heater and you’re going to have to pay a plumber to come out and fix it.

Thankfully, if you’re in this same position, you won’t have to worry about either of these things by the end of this post. I’ll show you the super-simple steps to drain and/or refill your boiler to correct a high or low pressure error and get your hot water working again.

How To Drain and Refill A Baxi Boiler

If you came across this post, you probably have a Baxi boiler or some other kind of combination boiler of your own and you’re Googling answers because the user manual sucks. It seems like there is no information out there on these boilers, so if something goes wrong you’re pretty much shit out of luck. Yep, same boat.

Basically, the machine we’re dealing with a gas-powered water heater that hangs on the wall and heats water on-demand, rather than storing it in a big tank like a traditional water heater. The one we have is the ‘Baxi Luna 3 Comfort’ model, which also handles our home’s heat.

Since we moved into our house during the summer, we had the hot water temperature set pretty low and it was no problem. In the winter, I like to take baths that basically scald my skin off, so I was messing with the settings trying to get the temperature a bit higher.

I was turning knobs I had no business turning, and suddenly I heard a hissing noise. The pressure gauge dropped all the way to zero, the machine clicked off, and an error message started flashing on the screen.

I walked over to the sink and turned the hot water knob. The water ran ice cold.

Fuck.

So, I did the logical thing and pulled out the user manual (which our angel of a previous owner left for us) and looked up the error code. According to the manual, I was supposed to turn a knob to refill the boiler and get the pressure back up. The problem was, the picture in the manual looked nothing like our actual machine, so I had no idea where the drain or refill knobs were.

Here’s what the bottom of our boiler looks like:

No matter how many times I turned the manual sideways or upside down, it didn’t look remotely similar. Even Googling didn’t get me very far; every video I came across was for a regular water heater or a different setup of boiler than we have.

Finally, after two hours of fiddling with the machine and almost breaking down in tears over the thought of taking cold showers until a plumber could come, I found a different knob that was hidden higher up than the rest and didn’t really look like a knob at all. I turned it, and once again heard a hissing noise. I looked at the pressure gauge and hallelujah—it was going back up.

So, here are the DRAIN and REFILL knobs correctly marked:

Using these knobs–DRAIN to lower the pressure and REFILL to raise it–should solve your pressure problem. Just make sure the machine is powered off before you use them.

I’ve read that if the pressure continues to be a persistent problem either getting too low or too high, that means you probably need to replace a part (which you can also do on your own with a little Googling).

Good luck!