Boiler pressure
- Thread starter ajs123
- Start date
Sponsored Links
Yep. Perfectly normal. It’s called expansion. 
As above, the hot water expands, increasing the pressure. The boiler will have an expansion vessel that has a diaphragm inside. As the water expands the diaphragm allows the volume to safely expand. As the pressure drops, the air behind the diaphragm pushes it back.
Only thing to add would be that the EV may need a little adjustment, time for a pre-charge pressure check. Normal pressure swing would be 0 > ~0.3 bar. Any more would indicate that either the EV may be be getting low on pre-charge or the vessel may need to be a bit larger (system size dependent).
When was the last time it was serviced and did they check the vessel?
When was the last time it was serviced and did they check the vessel?
Sponsored Links
- Joined
- 26 Oct 2023
- Messages
- 20
- Reaction score
- 8
- Country
You need a new plumber then.
Then you need a better service engineer
Get someone who knows what they're talking about to do it next time. Forgot to ask, is this rise in pressure a new thing or has it always risen that much?
Contrary to popular believe boiler servicing, when performed correctly, is a preventative measure, rather than it actually fixes things. It allows the engineer to get ahead of things that may be starting to show themselves.
If the EV is down on pressure then he obviously didn't check a serviceable item and if it continues to drop then the boiler pressure may eventually get to the point where it lifts the PRV. If it does that, the valve may also need replaced. Adding to your costs. Caught early during a service would avoid all of that.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
