apologies, im new to this so Ive had a quick youtube/google for knowledge.

I have a heatrae megaflow boiler in a all electric flat

looking at the boiler it has 2 thermostats elements immersion as above

last year the boost switch which gives me extra hot water failed so i ignored it, the boost switched on gave extra hot water when needed.

Last week the 2nd thermostat stopped working, so no hot water, So i called a plumber and paid a 90 call out fee, he had a look and quoted me 700ish parts labour, 2 thermostats or immersions elements thingy and boiler drainage.

I said id think about it, as i thought it was very expensive . I bought a thermostat online from you tube knowledge for 25.00 quid its a original or oem part.

I fixed the thermostat in the top spot of the boiler, i believe this controls the boost function.

But when the hot water gets hot, water squirts out from the thingy and into a open pipe, so I have to switch off the boost and use the hot water to stop the squirt.

this is the thingy and you can see water in between the ********

can anyone tell me why hot water come out and if that is normal? if it is not normal then what do I need to do to make it normal,

Im thinking change the thermostat from the boost and place it in the bottom slot, ?