I have not been to a Flowmatic that cannot be repaired. And who are the tenants to demand replacement.
OP, you are paying for your folly. What you have is a breakdown contract- your boiler, am certain, has not been service for many a moon. Neighbour across the road has a Turbo which predates the Flowmatic. He is told by one and all that arrives in the blue van that it should be replaced. He tells them to get the finger out out do the work they are being paid to do.
Get an independent to overhaul the boiler and tenant to shut up.
OP, you are paying for your folly. What you have is a breakdown contract- your boiler, am certain, has not been service for many a moon. Neighbour across the road has a Turbo which predates the Flowmatic. He is told by one and all that arrives in the blue van that it should be replaced. He tells them to get the finger out out do the work they are being paid to do.
Get an independent to overhaul the boiler and tenant to shut up.