We recently had the landlord and plumber round to replace our immersion heaters (plural - we're on economy 7) as both had packed up - the elements had split and shorted.
When the plumber replaced them, he put in new thermostats. Ever since, the hot water hasn't been as hot as it was before. It's most noticeable with the shower. The plumber reckons it's a venturi-style mixer, and before the work we used to have the dial about halfway round for a hot shower, now it's just hot enough when turned to the hottest setting.
This is with the immersion thermostat turned up full.
We had the plumber back, and he flushed through various pipes in case there was scale blocking the hot water pipes, all to no avail.
I've swapped the peak and off-peak thermostats (we never use peak), but it's no better. I had the landlaord round, he ran his hand under the tap and declared it fine. I brought home a digital thermocouple-type thermometer from work and the hot tap gets to a maximum of 55.8°C in the morning when the immersion heater is still on (running the tap for a few minutes).
The landlord brought round another thermostat to try, but the hot water gets to the same temperature.
The thermostat is a Heatrae Sadia 7-inch one. The instructions say it comes with the dial preset to 60°C, and it was somewhere in the middle. With it turned all the way up, we get no hotter than 56°C.
We now don't know what to do - the landlord's getting annoyed at calling out the plumber and not finidng out what's wrong, and we're getting annoyed with warm showers.
Can anyone suggest something to try? Are there different sorts of thermostats - could we get a hotter one? The ones we have audibly click in the middle of the dial range at room temperature (i.e. out of the water tank) - is that right?