The Junior range are a pig to service and the heat primary heat exchangers are pants. Other than that they are pretty reliable.
Really?
I've replaced nearly every part in these over the years, both hydro blocks, pumps, gas valves, fans, pcb's, turbine adapters galore.
In fact I think the only part ive never replaced due to failure is the electrode leads, although replaced one set because a mouse had chewed through it!