Worcester Bosch 350 pressure

[phi]

The pressure has suddenly been rising over 3 bars on my boiler and an engineer replaced the expansion vessel last week. Despite the new vessel, it is still rising and the pressure relief valve is striggered when the pressure reaches over the 3 bar.

Once the boiler is cold the pressure only marginally goes back down and stays at around 3 bars. I have to let water out manually to take it back to about 1.2 bars about 4 times a day.

When cold, the boiler pressure has always been set at 1.2bars. The (12 year old) system has been flushed every year + has protector fluid in it to prevent scale etc. Most rads were flushed out 6 months ago. There is no air in the radiators, all the rads come on hot and we have hot DHW. There are no whining noises or bangings coming from the boiler. The room thermostat works and the boiler shuts down at the required temperature. The filling loop is disconnected thus there is no cold water seeping into the system.

The DHW heat exchanger is also new. The expansion vessel was already replaced over 2 years ago and worked fine after that.

I think the engineer said that the expansion tank gets hot which means the water is reaching it - i.e. there is no blockage preventing excess water getting to it.

Any idea what could be the cause of this sudden pressure constantly rising. Another faulty expansion vessel?

Many thanks.

Phil

 

[chrishutt]

Sounds like a leak from the cold mains side to the heating system side. Since you've disconnected the filling loop, the likely culprit is the DHW heat exchanger. Does the problem date from when this was renewed? Are you sure a new one was fitted (not an old reconditioned one)?

Easy to test this - turn of the cold supply into the boiler (should be an isolating valve on inlet connection). If pressure then stabilises it's a leak from that source. If pressure continues to rise....?????

 

[phi]

I had thought about it but dismissed it as the DHW heat exchanger was replaced new by Worcester. No reason to believe it was not new unless there is new and old in the back of the van...

However, in as much as I keep emptying the boiler and yet it is still full of water then this is probably the reason. Other way to find out is to turn off the mains and see.

Temporarily turning down the mains pressure could cause it to go the other way if system pressure was higher than mains and then CE water flowing back into DHW which then becomes contaminated. Can't fill the kettle with that! Freaky.

Thanks for your pointer.

Update 2nd Jan 06 - Yes it was the DHW heat exchanger. Replaced it a few days ago and working well now.

Phil