We have a combi boiler which is working perfectly. We only have hot water through the upstairs shower but if we run the tap in the sink in the shower room and then turn off the shower we have enough hot water in all the taps in the house to last for a while. Could this be the shower cartridge in the upstairs shower?

I don't think I follow your post. Are you saying that you don't have hot water at the tap until you run the shower for a while?

I don't think I follow your post. Are you saying that you don't have hot water at the tap until you run the shower for a while?

The upstairs shower always works, the hot water taps run cold (or lukewarm) but if we turn on the shower room sink tap while the shower is running then the water runs nice and hot and if we leave that tap running and turn off the shower then the water is hot for a good while in all the taps in the house.

Don't know much about combination heating and domestic hot water systems but it sounds like you either have a faulty mixing valve or you have a recirculation pump and line and the pump is faulty.

The temperature balancing valve in the shower works off pressure not temperature. Chances are that if you run water from the hot tap for a while, (just like you are doing in the shower),the hot water will eventually get there, and to all other taps upstairs. You will then have the hot water for a while, just as if you had open the shower valve.

Don't know much about combination heating and domestic hot water systems but it sounds like you either have a faulty mixing valve or you have a recirculation pump and line and the pump is faulty.

The temperature balancing valve in the shower works off of pressure not temperature. Chances are that if you run water from the hot tap for a while, (just like you are doing in the shower),the hot water will eventually get there, and to all other taps upstairs. You will then have the hot water for a while, just as if you had open the shower valve.

We can't get hot water anywhere else unless we go through the whole rigmarole of running the shower etc etc etc and then the hot water only lasts for a while.