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Discuss pressure loss pressure gain in the Central Heating Forum area at PlumbersForums.net

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Hi all

I have a Halstead combi boiler in the loft about 12 years old, every week I have to raise my pressure back up as it nears zero, this has been ongoing for around six months.

I have recently started putting my heating on, when I turns it on I get an error code 3 for a few seconds, then it goes to normal. But In the space of around 5 minutes the pressure shoots up to 3 so I have to turn the heating off. When it goes over pressure 3, the copper pipe outside dripped a few times.
I also feel a strong gust of wind when I am in the attic near my boiler, and the heating is on. Not when it is off though?

Last year when the heating was on, after around 40 minutes into it one hour cycle it made a loud motorbike noise for short while as it was ready to turn off. I haven't tested it for this long yet this year.

On top of this, this past week my radiator has started to drip - only very slightly, about 3-4 tiny drips an hour. Unrelated to the pressure drop as the pressure drop was happening before.

As an aside, my actual water pressure is quite fast and I have had to reduce it slightly via the stop tap. but its still so fast the pipes knock when the water comes in to fill the washing machine or stop filling it. Could this cause an issue?

Could using the taps quite often whilst showering/using washing machine flushing toilet, etc all at once, cause an issue? We have a large family.

Sorry for such a complicated post, it would be helpful for any thoughts.

I will hopefully be getting the plumber in soon.
 
Pressure shooting up to 3 in a short space of time indicates an expansion issue. Regards the pressure drop, could be a rad, or even the pressure relief valve. You’ll need a gas safe registered engineer to sort the expansion issue and potential prv failure.
 
1. If you have been re-pressurising the system for 6 months, you will have fed aerated fresh water into it. This makes it quite likely that the radiators will start to rust from the inside out. The leak needs to be identified and stopped. I would then advise you to flush the system. In my opinion this is best done be power flushing, but you could try a chemical flush to save the cost. Take the opportunity to fit a magnetic filter on the return pipe to the boiler as close to the boiler as you can get it.
2. The pressure rising fast suggests that the expansion vessel either needs its air charge replenishing, or that the expansion vessel has become faulty.
2a. Only a Gas Safe registered person can work on gas appliances, and such work can include merely removing the cover of the boiler, depending on its construction.
2b. If you can safely reach the cap on your expansion vessel (looks like the cover on a car tyre valve), unscrew it, and depress the top of the valve inside. Again, its the same type of valve as a car tyre. If more than a tiny amount of water comes out, the vessel needs replacing.
2c. If it still has air in it:
2ci. De-pressurise the system. With a loft boiler this will probably only mean draining the boiler. Leave the drain point open.
2cii. Use a car tyre pressure gauge to measure the air pressure in the expansion vessel. If its below the boiler manufacturers set level, pump it up with a car type tyre pump. If you don't know the level, 1.0 bar is a reasonable working figure.
2ciii. Replace the cap and re-pressurise the system.
3. Because your pressure relief valve has operated, there is a good chance it won't re-seal. Keep an eye on the copper pipe outside. If it drips, you will have to get the PRV replaced.
4. By "fast water pressure" I assume you mean a high flow rate. Part closing the stop tap won't alter the pressure, but it will reduce the flow rate.
5. If your pressure (which drives the flow rate for a given set of circumstances) is too high, the only way to lower it is to install a pressure reducing valve.
6. The radiator leak may have been caused by excessive pressure in the system (not you mains water pressure). Fixing / replacing the expansion vessel and / or PRV may stop the leak. I would doubt it and suggest you investigate and resolve the problem. Might be no more than tightening a nut or two.
 
Hi,

this is the original poster but I can't find my login details and couldn't find this thread until I have found it in search.

An update.

I called an engineer who came out and pressurized the expansion vessel which sorted the pressure going up. However it was still going down.

I had a small leak fixed in one radiator by a plumber a few days later as it was leaking a tiny amount from the bleed valve.

Another engineer came out and replaced the gas valve, did a service and put leak fluid into the system. This slowed the loss down. However a day or so later I noticed there was after a deep humming in the pipe when the hot water was turned on, this went a few days later to be replaced with a different noise in the pipes and radiators when the hot water tap was used and turned off and the boiler still running (cooling down fan for around 4 minutes).
Now the copper pipes and radiator is making a running water sound when the heating is turned on.

I also hear a sharp shut off knock under the bathroom floorboard whenever my downstairs washing machine is filling up as it contracts the pipes.

I think I need inhibitor as I asked the engineer to do it during the service but don't think he did.

What can I do next - exasperated. Thank you
 

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