The Shower Doctor Surgery: How to service Gummers 1500

This guide will explain how to fit a seal kit to a Gummers 1500 series valve. This is a very popular valve that is used by various manufacturers.

Each has put its own knobs and handles on it, so it can look very different on the outside. When it comes to servicing the valve however, the internal components are all the same.

The how-to video that accompanies this guide shows a valve with a plastic knob set. If you have the chrome-plated Victorian style valve, you'll need to remove all the handles first.


Before you start you'll need to switch off your water supply and dry your shower area thoroughly to avoid any accidents. You should also place a towel or rag over your waste pipe to prevent tiny screws and components from falling down it.

You will need a few different tools to service your valve depending on the style you have. This may include an Allen key, a flat-headed screwdriver, an adjustable wrench, a pair of plug pliers and a tool with a small point.

Disassembling the valve

If your valve is the same as, or similar to, the one shown in our instructional video, you can begin by removing the front cap. You'll be able to flick it off with your fingernail or a small screwdriver.

Underneath you'll see the screw that holds the knobs in place. Unscrew this using an Allen key. In some models you'll need a flat-headed screwdriver. You'll find a small O-ring at the base of the screw, so take care not to lose it.

Then pull the plastic knob forward and off, followed by the shroud and the metal retaining ring. You may need to use a screwdriver if they are tight. Next remove the cartridge using a pair of plug pliers or a wrench to unscrew it.

Behind the cartridge is the wax capsule that controls the thermostat function, the piston and a spring. The easy way to service the valve is to buy a new cartridge, piston and spring together as one assembly and simply replace it. This is however, more expensive than simply replacing all the seals.

Disassembling the cartridge

Begin by taking the bottom part off the cartridge. Grip it with a pair of pliers or a wrench around the middle part, then take a screwdriver, an old flat piece of metal or any tool that will pass through the holes at the top of the cartridge to hold it in place while you unscrew the bottom.

Next take the inner workings out of the cartridge by removing the circlip and pulling them out. You might need to tap the end with the handle of a screwdriver if they are tight.

Now simply unscrew the spindle from the inside part of the cartridge and place a small screwdriver into the hole to remove the temperature adjustment screw. That is the cartridge disassembled.

Replacing the seals

Open up your service kit and lay out all of the new seals on your workbench. You may not need all of the seals in the kit depending on the type of 1500 valve you have.

Remove the old seals from the cartridge parts one by one using a pointed tool, replacing them with the corresponding seals from the pack. Discard the old ones straight away to avoid getting them mixed up with the new ones.

A good way to make sure you're using the correct seal for each part is to place both the old one and the new one onto a screwdriver and let them hang down. This way you'll be able to see whether they are the same size.

One of the hardest seals to replace is the one that fits into a recess in the bottom of the inside part of the cartridge. If this seal is damaged it can cause the shower to drip.

You'll need to use a pointed tool to prise it out, and when you put the new seal into place you'll need to warm it up and soften it first by popping it into a cup full of very hot water for 30 seconds.

Slowly push it into place all the way around. The handle of a screwdriver will be useful to get the final part of the seal in, as it can be very tricky.

Reassembling the cartridge and valve

When reassembling the cartridge, make sure you grease all of the moving parts and the seals as you go. Grease is supplied in the seal kit, or you can buy The Shower Doctor's own silicone grease.

Begin by popping the temperature adjustment screw back into the inside part of the cartridge and securing it with your screwdriver, and then screwing on the spindle.

Now push everything back into the body of the cartridge and screw on the bottom part, using a wrench to tighten it up, before replacing the circlip.

Before you place your cartridge back into the valve, there are two more seals that need to be replaced in the same way that you replaced the others - one at the front of the valve and one towards the back.

Once that's done, pop the wax capsule back into the base of the cartridge, followed by the piston and the spring. The spring will have a tendency to fall out as you push everything back in, so it's a good idea to prise the end of it out just slightly so that it fits into the piston a little more snugly.

Now screw the cartridge assembly back into the valve and tighten it up using a wrench or a pair of plug pliers. Finally, place the plastic shroud and metal retaining ring back on, followed by the handle.

Make sure the valve is turned to off, then put the handle on at the off position. Place the holding screw on just slightly and then go and turn the water back on.

Once the water is on, check the temperature of the valve and readjust if necessary. You can then tighten the holding screw and pop the front cap back on to finish your service.

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