Hot water from taps but not from shower (combi boiler)

This could be three things. 1. Faulty shower thermostat 2. Could be a blocked plate heat exchanger which will make the boiler overheat on hot water. A shower has less of a flow of water than taps so this problem can only happen when the shower is operated. This would make the temperature on the boiler screen increase quickly and turn the flame off. 3. This isn’t likely but the boiler has a flow sensor that operates when a hot tap is open, if you operate the shower and the boiler doesn’t fire up with the tap symbol then the flow sensor is faulty and not recognising that the shower is on.

Most likely shower mixer problem

Hi, Regarding the info given and that you have hot water at your other h/w outlets it is highly likely the thermostatic shower valve will be at fault. A few quick simple checks from a plumber will determine this for definite. Fensure Plumbing sevices

🔧 1. Shower mixer valve problem • If your shower is a mixer type (especially a thermostatic mixer), it might be stuck or faulty, not allowing hot water through. • Sometimes after a boiler repair or water supply disruption, debris or scale can block the thermostatic cartridge. What to try: • See if the shower gets warm when set to full hot. • Check other taps in the bathroom — do they get hot? • Try running the boiler while someone else turns the shower on to see if the boiler responds (flame symbol or burner light). ⸻ 🔥 2. Boiler not detecting demand from shower • Some showers (especially digital or pumped ones) may not trigger the boiler properly. • If the flow rate is too low, the boiler might not “see” the demand and fail to fire. What to try: • Turn on the shower and observe the boiler — does it ignite or show any sign of operation? • Check if the hot water light comes on (or listen for the boiler firing). ⸻ 🚿 3. Blocked showerhead or filter • A blocked showerhead or inlet filter can reduce flow, stopping the boiler from activating. • This is a very common issue after plumbing work when debris gets into the system. What to try: • Unscrew the showerhead and run the shower — do you get hot water now? • Clean out any filters or strainers on the shower. ⸻ 🔄 4. Airlock in hot water line to the shower • After work on the boiler, an airlock could be affecting only the hot pipe going to the shower. • This can prevent flow and activation of the boiler. What to try: • Try running both hot and cold taps/showers at full flow to try and flush out air. • Sometimes connecting a hosepipe between hot and cold taps and backflushing can help (only if safe and you know how). ⸻ 🧰 5. Boiler settings or diverter valve issue • The diverter valve inside the boiler controls where hot water goes. • If it’s partially stuck (e.g., due to debris or the recent repair), it might not send hot water to the shower properly. What to try: • Run a hot tap and check the boiler’s behavior — then turn on the shower and see if it behaves differently. • If the boiler heats the water fine for taps, but not for the shower, this is less likely unless the diverter is failing selectively.

The thermostat on the shower needs replacing .

If its a thermostatic controlled shower the mixing valve inside the shower could be faulty blocked up on hot side hence no hot water coming the cold could be Bypassing and entering the cold aswell best thing to do is replace the shower

Generally speaking from my experience over the 8 years I've been plumbing, if you find every appliance works fine besides one appliance, it's usually that appliance that's the issue. In this case the shower. The next question is wether this is a thermostatic shower, bar mixer shower etc.. thermostatic and bar mixers can often have an issue where the temperature will not regulate, either it stays tepid or cold. Usually this is a simple cartridge change. It's usually a thermostatic cardige. This is rare but can be an issue but that's if the pipework supplying the shower is too big. A flow restrictor on the shower hose can stop this. However, it would be an issue that's always happened, not just happened. In your case, I would say it sounds like the shower is at fault. If you wish for me to provide any other details. Feel free to contact me.