You need a G3 qualified plumber, not a builder.
When you say cyl stat clicks at 30° do you mean when you rotate it manually?
That would be normal as it will click when you go below and above the temperature it is currently at!
Do you have a gas heat source (boiler)
Is it a heat only or a...
Fitted a ravenheat to a 5 storey cast iron stack... Put the condensate so it went into the sink and was diluted by the hot water... No heating. So I did it but at the time thought it could be questioned ;)