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Hi all. This is my first post, and I'm a homeowner and not a heating engineer or plumber, so apologies if my knowledge is a bit off.
To give a bit of history we had a problem with water hammer in our pipes so had a pressure reducing valve fitted under the kitchen sink. The local water company had measured the water pressure coming in to the property at 4.5 bar, and when the valve was fitted and set at 2 bar, the water hammer problems stopped. So far so good.
After a while we started to get what was seemingly randomly timed loud vibrations in our pipes. It soon became apparent it only happened when opening the kitchen sink mixer tap, but not all the time. Over time it settled into a pattern of hot water going on, the pressure reading on the valve slowly rising from 2 to over 4 bar, and then when the kitchen tap was turned on, a loud vibration, and the pressure going back down to 2 bar. But again the noise didn't happen every time the pressure dropped. I'm not sure about this, but having looked at a few websites, the noise may have been the valve trying to handle the backflow pressure out of the system?
Anyway the noise is a problem, but the main concern was the rise in pressure (get rid of the cause, and get rid of the effect at the same time). Having looked into possible causes we settled on the white expansion tank on the unvented cylinder upstairs not doing it's job. So we had a heating engineer come out to have a look at it (under our annual maintenance contract). He found that there was no pressure in the tank, and recharged it. Since then, not only has the pressure risen as before when the hot water is on, but it also slowly rises to 3.5 to 4 bar when the hot water is off. Again using the kitchen tap at this time may result in a loud vibration and pressure drop to 2 bar. The central heating isn't being used at the moment.
So we're planning to get an engineer back, but I'm trying to understand what's going on before we do. The engineer spotted some info on the side of the expansion tank, eg. 6 bar max pressure, and also a picture showing 3.5 bar. So he pressurised the tank to 3.5 bar. Should he have actually pressurised the tank to 2 bar to match the pressure reducing valve setting? My basic understanding would be that when the hot water is off, and the water in the system cools and lowers pressure, the higher air pressure in the tank will push water out of the tank, and raise the water pressure in the pipes above the 2 bar we want. I'm also wondering if the 3.5 bar icon refers to the pressure the tank was shipped with after manufacture, not a suggested pressure. It's not easy to tell as the pictures on the side of the tank are partly obscured by the centre seam of the tank. Or does this behaviour suggest something is wrong with the tank?
Not really having any experience in this area what I'm thinking could well be completely wrong, but on the other hand I'd really appreciate any comments or suggestions that I can put to the engineer. Ideally having an annual maintenance contract should mean that we can depend on their engineers' advice, but I'm not sure what the first engineer did was actually the right thing to do. Thanks, and sorry it's a bit long!
To give a bit of history we had a problem with water hammer in our pipes so had a pressure reducing valve fitted under the kitchen sink. The local water company had measured the water pressure coming in to the property at 4.5 bar, and when the valve was fitted and set at 2 bar, the water hammer problems stopped. So far so good.
After a while we started to get what was seemingly randomly timed loud vibrations in our pipes. It soon became apparent it only happened when opening the kitchen sink mixer tap, but not all the time. Over time it settled into a pattern of hot water going on, the pressure reading on the valve slowly rising from 2 to over 4 bar, and then when the kitchen tap was turned on, a loud vibration, and the pressure going back down to 2 bar. But again the noise didn't happen every time the pressure dropped. I'm not sure about this, but having looked at a few websites, the noise may have been the valve trying to handle the backflow pressure out of the system?
Anyway the noise is a problem, but the main concern was the rise in pressure (get rid of the cause, and get rid of the effect at the same time). Having looked into possible causes we settled on the white expansion tank on the unvented cylinder upstairs not doing it's job. So we had a heating engineer come out to have a look at it (under our annual maintenance contract). He found that there was no pressure in the tank, and recharged it. Since then, not only has the pressure risen as before when the hot water is on, but it also slowly rises to 3.5 to 4 bar when the hot water is off. Again using the kitchen tap at this time may result in a loud vibration and pressure drop to 2 bar. The central heating isn't being used at the moment.
So we're planning to get an engineer back, but I'm trying to understand what's going on before we do. The engineer spotted some info on the side of the expansion tank, eg. 6 bar max pressure, and also a picture showing 3.5 bar. So he pressurised the tank to 3.5 bar. Should he have actually pressurised the tank to 2 bar to match the pressure reducing valve setting? My basic understanding would be that when the hot water is off, and the water in the system cools and lowers pressure, the higher air pressure in the tank will push water out of the tank, and raise the water pressure in the pipes above the 2 bar we want. I'm also wondering if the 3.5 bar icon refers to the pressure the tank was shipped with after manufacture, not a suggested pressure. It's not easy to tell as the pictures on the side of the tank are partly obscured by the centre seam of the tank. Or does this behaviour suggest something is wrong with the tank?
Not really having any experience in this area what I'm thinking could well be completely wrong, but on the other hand I'd really appreciate any comments or suggestions that I can put to the engineer. Ideally having an annual maintenance contract should mean that we can depend on their engineers' advice, but I'm not sure what the first engineer did was actually the right thing to do. Thanks, and sorry it's a bit long!
