Water not hot enough

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Fellas,
I have a one house i rent out to my ex neighbours who are now my tenants.
3 or 4 years ago i got a new boiler for them, a saunier duval combi.
They complain about the water not being hot enough, i went round before and water was hot enough for me, radiators were scolding..

But they tell me when boiler was first installed, water was piping hot all the while, now it just pleases itself when it wants to get hot, any ideas??

 

[corgiman]

when was the last time it was serviced, who wrote out you LSC?

could be DHW thermister

 

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Corgiman thanks for reply, can you elaborate a little??