I have a saunier duval boiler - the needle on the dial is very near to the red zone on the right. It was fine before I had it serviced - then the needle was going into the red zone. That engineer said to call him if this happened. He came out and released some water from a pipe and said if the same thing occurred it would be very expensive! I called another engineer (as I no longer trusted the first one) and he said it was leaking water at the external outlet. He replaced a part, but now the needle is close to the right red zone on the dial. Before I call another engineer, can anyone give me an opinion or any advice as to what to do. Thanks in advance

Hild Liptrott, July 2009

Thanks for reply - its a Thema F23E

Hild Liptrott, July 2009

as problem only happened or seemed to happen after service, i would be first looking at the external filling loop, try disconnecting the braided hose between the valves,and capping off. could be that when he serviced he topped up pressure with filling loop and now its passing, building up pressure. expansion vessel only really comes into play when boiler is on central heating.
what model sd u got??

Andy, July 2009

It's safe to use, it just means that if it goes into the red some water will discharge out of the pressure relief pipe (copper pipe which usually sticks out a few feet below the flue)

Ian, July 2009

Hello again - just one more question. I will get a boiler engineer around this week, but in the meantime if I use the hot water and it goes into the red what would happen, is this dangerous, and will it damage the boiler further.

Hild Liptrott, July 2009

Many thanks for your advice

Hild Liptrott, July 2009

If it just needs to be re-pressursed then it should only take about 15 mins, and shouldn't be that expensive. However if the expansion vessel or diverter valve need replacing it'll be more expensive.

The easy way to tell if it's the expansion vessel that's faulty is to try the following.
Drain some water out of the system until the pressure is around 1 to 1.5 (use the drain point or bleed a radiator to do this)
Take a note of the pressure and then leave it for half an hour or so and make sure it's the same (if it has increased the the diverter valve or the filling loop is passing water into the heating)
If it's the same then turn on the heating, if it increases a lot (into the red) then the expansion vessel is faulty, or the pipe running to it is blocked.

First thing to try is re-pressurising the expansion vessel as i said earlier (to around 1 or 1.5 bar). If it reads 0 pressure before re-charging, and holds the charge then that should sort it.

If the vessel is burst or the diverter valve needs replaced, prob best to phone british gas and ask for a fixed price repair, as this will work out cheaper as the parts are expensive.

Ian, July 2009

I really appreciate your answer. I will need to get a boiler engineer to do this. Do you have any idea of what they would charge to do this.

Thanks again

Hild Liptrott, July 2009

Sounds like the expansion vessel may need to be re-pressurised. This is done by draining the boiler & re-pressurising the expansion vessle with a footpump. If it's not holding the air then it will need to be replaced. If expansion vessel is ok, then the diverter valve may be passing the mains water into the heating, in which case it will need to be replaced. The only other thing to check is that the filling loop (the pipe you use to top up the pressure) is closed off fully.

Ian, July 2009