Central Heating boiler pressure

brn1

I have a Mynute 14-48 SEwall mounted boiler and the pressure, when running, is 3-4 bar and it discharges outside. I recently had an attic conversion with a radiator added and since then I have had this problem. The boiler was serviced and the 3 bar prv was replaced at the time but it still hasn't solved the problem. Any advice? Thanks.

beldin

If the pressure goes over 3 bar then the pressure release valve will kick in.
Was the pressure vessel checked. Red thing with a inner tube valve on it.

ircoha

brn1 wrote:

I have a Mynute 14-48 SEwall mounted boiler and the pressure, when running, is 3-4 bar and it discharges outside. I recently had an attic conversion with a radiator added and since then I have had this problem. The boiler was serviced and the 3 bar prv was replaced at the time but it still hasn't solved the problem. Any advice? Thanks.

check to see that the valve on the cold water feed/top-up loop is closed.i suggest this as if the system is closed then it should not blow out every time: the water seems to be being replaced

JamesM

ircoha wrote:

check to see that the valve on the cold water feed/top-up loop is closed.i suggest this as if the system is closed then it should not blow out every time: the water seems to be being replaced

That looks like it. It must be connected to the mains. Each time the heat goes off, the water contracts and it takes in water. When the system heats again the water expands and blows off. Turn off the cold water feed. Fill every few months if needed to keep the pressure at about 1 bar.
Jim.

brn1

JamesM wrote:

That looks like it. It must be connected to the mains. Each time the heat goes off, the water contracts and it takes in water. When the system heats again the water expands and blows off. Turn off the cold water feed. Fill every few months if needed to keep the pressure at about 1 bar.
Jim.

Hi I've done this and released the pressure but it just goes back up to 3 bar. I can't think where the water is coming from.

JamesM

brn1 wrote:

Hi I've done this and released the pressure but it just goes back up to 3 bar. I can't think where the water is coming from.

If you've found the correct valve and turned it off, the pressure should drop.
Have the heating turned on, so that the water has expanded, then turn the safety valve and release some water - until the pressure is just above 1bar. If it goes up to 3 again, you must not have the cold feed turned off.
Jim.

brn1

JamesM wrote: »

If you've found the correct valve and turned it off, the pressure should drop.
Have the heating turned on, so that the water has expanded, then turn the safety valve and release some water - until the pressure is just above 1bar. If it goes up to 3 again, you must not have the cold feed turned off.
Jim.

I've checked the cold feed and it's off. Could this problem be caused by a faulty pressure vessel? Thanks

JamesM

brn1 wrote: »

I've checked the cold feed and it's off. Could this problem be caused by a faulty pressure vessel? Thanks

If the pressure vessel is faulty and the diaphragm has burst, then there is no expansion and the pressure will go very high. But if you let water out and get the pressure down to 1 bar, when the system is hot, as far as I know, there is no way that it can go back up to 3 bar, unless extra water is getting into the system.
I suppose there is a chance that when the water cools and contracts, the system might suck in some air - then when the system heats again, the pressure could build up. If that is the case, you should find that you have a lot of air in the system - probably in the upstairs rads.
Normally the diaphragm in the pressure vessel only bursts if the vessel is old (15 or 20 years) or the water in the system has boiled and weakened it at some time over the years.
Also, you may have a faulty valve at the cold feed that is letting water through.
Jim.

brn1

Thanks to everyone for their advice. I reckon the stop valve on the top up line is the problem. I managed to reduce the pressure down to 1 bar last night and when I checked this morning it was up to 2 bar with heating off since last night. One question, as the top-up pipe is feed direct from the main, would the water pressure be too much and force its way past the stop valve, and does the stop valve on the mains need to be fully open?

JamesM

brn1 wrote: »

Thanks to everyone for their advice. I reckon the stop valve on the top up line is the problem. I managed to reduce the pressure down to 1 bar last night and when I checked this morning it was up to 2 bar with heating off since last night. One question, as the top-up pipe is feed direct from the main, would the water pressure be too much and force its way past the stop valve, and does the stop valve on the mains need to be fully open?

No water should get past a stop valve if it is working properly, no matter what the pressure. The way I set the mains stop cock is to turn on the kitchen tap and adjust the stop cock to give me the required pressure. I think that I have it a bit less than half way open. I want a good bit of pressure in the sink, but not splashing all over the place.
Jim.