Triton T80 Wont Heat Water

I would check that flow rate myself, turn the temperature control to fully cold then with the shower head in place, switch on the shower and hold a container under it for exactly 15 secs, measure this with a 1 litre milk bottle or whatever, X4 to give the flow rate in LPM. My T80Z Fastfit requires 4.5/5.0LPM to start heating but flows 7.5/8.0LPM doing the above test. There is no low pressure/flow LED on mine but it does have a crude indication in the form of a red (semaphore) flag which shows red in the window and disappears when the flow is OK but not really a good indication as it can be "nearly" invisible but the heating element contacts are still open, a real low pressure LED is fed from contacts on one of the microswitches.

Do that flow test again and if OK and you can use a multimeter can suggest a test or two, TCO etc. If the flow is ~ 4/5 LPM, turn the power switch to select one element, then very slowly turn the temperature control towards hot and see if the water starts heating.

Removing the cover does nothing to the pressure valve or TCO. In other words removing the cover can't effect the temperature in any way.

In Ireland mains fed shower should be fed from the cold water tank in the attic & pumped to the shower. In parts of Dublin most homes can't get hot water from a mains fed shower on the ground floor. Less again on the next floor. Only a cowboy would attempt to run a shower directly from the mains in the attic in Dublin.

You issue is most likely water pressure problems due to an incorrectly installed shower. Extremely unlikely to be a faulty shower

When you turn it on does the flow indicator change colour at all? It should change colour if you have enough pressure. If it doesn't change colour then it's either not installed correctly or you don't have enough pressure.

Try it at midnight when mains water demand drops off. If you get warm water then you have proved it's a pressure issue. Another test is to cover the shower head with your head for 8 seconds or so. Let go but keep a hand in the flow of the water. If it gets warm for a few seconds then it's a water pressure problem. It could take another 10 seconds for the warm water to reach the shower head