Shower runs very hot then trips power

Sounds like the heater element is nearing failure, and drawing excess current (and hence heating more than expected)

Probably not (unless you have the shower connected to the hot feed from the combi)

The head is possibly in need of descaling.

Try it without the shower head. If it still trips then it is probably the element that is scaled up or failing in some way. If it is ok in this mode then it will be as stated - the head needing a good clean.

Thanks for the quick replies chaps!

Mark

Its possible you have two separate faults. The running hot caused by scaling and the tripping caused by a bad contact at the MCB end, either busbar or conductor, accelerating the thermal trip. If not competent to check out the MCB get an electrician in who would be able to measure the actual current against the shower rating.

Jim A

While this is possibly true, the "trip" you get from overtemp of the water would be a thermal safety cutout in the shower itself. You should not get a MCB trip as a result of this, since how hot the water gets should not influence the current drawn by the heater - the water temperature is dictated only by the flow rate.

Jim's observation about a loose connection in the CU is also well worth investigating.

If you have a clamp meter (or can borrow one), sticking it round the wire coming out the top of the MCB in the CU so that you can see the actual current being drawn will give you a much better starting place to work our what is going on.