This VC series diverter valve was fitted to most Stiebel Eltron Ground Source units, and many others. It diverts the flow to either heating or hot water (DHW) modes. (it’s either/or and does not blend).
It is not uncommon for them to stick either half-way, or stick in DHW mode.
It’s incredibly easy to remove the grey motor head by pressing the silver button and twisting it out like a bayonet light bulb. The valve spindle can often be freed-up by pressing it (gently but firmly) with the side of a big spanner or something.
I have noticed over the years that most engineers simply replace the whole valve, at great expense. However, the valve is very high quality. The bronze body should last for ever, and it is designed with a quality plastic cartridge that can be replaced very easily.
I find it very annoying that some perfectly good quality heat pumps can be deemed irreparable simply because of the very high cost of repair.. E.g. the £3 rotary encoder can fail on a controller, but the normal solution is a new controller for several hundred pounds. Finding someone to solder in a rotary encoder is probably impossible.
I came across a stuck valve recently, and no amount of pushing and pulling the spindle would free it up. I was determined fix it without great expense so researched replacement cartridges and was struggling to find the right cartridge, so took a gamble and ordered a £30 cartridge that should fit all 3-port VC types. They come with different ‘window’ openings, so I didn’t know if it would work. £30 seemed worth a punt. It also came with a small removal tool
The first hurdle was getting the old cartridge out. The picture shows the removed cartridge (left). It unscrewed, but refused to pull out. However a rubber ‘O’ ring was stopping it from coming out, so I had to ‘hook’ the ‘O’ ring out from the groove (red arrow) from down one of the ports using a very small screwdriver. I simply pulled the ‘O’ ring until it broke. With the cartridge removed, I could now see that my replacement had restricted ports, and I quite easily filed the slots out to make it match the original. Its a good rigid plastic. For next time, I will make sure any replacement has full-size, full-flow ports.
Below is my modified replacement next to the old sticking one. To the right looks like the correct replacement along with the removal tool/spanner.
If the valve body needs removing, as it no doubt will, then a good spanner as below will be needed to remove it.
The system has steel radiators and now has a magnetic filter, so hopefully there will be no more grunge build up on the valve, and hopefully the valve will not stick again.
If you are reading this, you might have a Stiebel controller. I came across one that always lost its memory after a power interruption. It was very easy to fix and the 0.1F capacitor easy and cheap to buy.