Gaggia Titanium

Hello,
my Gaggia Titanium coffee became "colder" from time to time. After a call to the workshop I was advised to uncool the machine first.
I did this with the result that a puddle formed underneath the machine. After the demonstration of the machine, the cause for the puddle is quickly found. It is, as often described in the forum, the steam valve. I have already ordered this and am waiting for its arrival. Costs approx. 50€
More headaches now the "cold" ( changing, tendency always colder ) coffee makes me.......
What could be the cause ? What steps should I take to narrow down the cause of the error? ( electronics, instantaneous water heater, temperature sensor, etc ...) There are certainly a number of possible causes.
Who knows the problem ?

Thank you very much for your advice and tips....

Greetings from Erlangen

Manfred