Do I need to replace my Vaillant VCW sine 18T3W combi boiler?
The pressure gauge on my Vaillant comb-boiler (VCW sine 18 T3WF H) has dropped to zero. When the system is refilled, the water leaks out.
On its service, the engineer said that the systems are too old and should be replaced. He didn't offer any solutions to the leak.
Can the system be repaired or should it just be replaced?
Everything can be repaired, as far as I am aware, everything is still available for the sine 18.
However, you fail to mention where the leak is coming from, therefore the cost of repair can't be assessed.
It may be that the cost of repair outweighs the value of the boiler, therefore throwing good money at a 25 year old boiler might not be the best option, without better information from you, unable to assist further.
Bear in mind that the running cost of a new boiler could also reduce the gas bill quite considerably.