Flat expansion vessel

[TNDU]

My 7 year old Worcester Bosch combi is making a right racket and the water pressure is at nearly 3 on the gauge when it gets to its top temperature of 72 degrees. The water overflows to the outside constantly to relieve the pressure but it doesn't really work.

I have a maintenance contract with British Gas, so the engineer came yesterday and said my expansion vessel was flat so he topped it up and tested it and it was all fine. However, this morning when I turned the boiler on, the same problem has occurred so the repressure of the expansion vessel didn't last very long.

Anyone can advise what the problem may be as it is obviously making the expansion vessel go flat all the time? Thanks.

 

[CountryFan]

Not necessarily the vessel going flat, could be a blocked communication pipe. I've had some vessels in Vaillants fail after 3 years as well. Best get BG back

 

[TNDU]

Not necessarily the vessel going flat, could be a blocked communication pipe. I've had some vessels in Vaillants fail after 3 years as well. Best get BG back

I have made an appointment for British Gas to come back but thought I should ask around so I am more knowledgeable about the matter.

So it could be something else causing the high pressure? As the engineer recharged the expansion vessel yesterday afternoon and it was fine after he did that, and it was back to its old tricks again this morning, you have to think that the expansion vessel has gone flat again as it seemed to have solved the problem for about 10 hours.

 

[CountryFan]

Yes it could have done, In which case it will require a new one. It could also be the pipe leading to it

 

[TNDU]

Yes it could have done, I'm which case it will require a new one. It could also be the pipe leading to it

one thing i did notice when the engineer left was that the boiler kept turning off and I had to increase the room temperature setting on the thermostat to 34 degrees before it would turn on again. but after it got to 21 degrees, which is my normal setting, i turned the thermostat setting down to 21 degrees, and it was fine after that, but without me messing around with the room thermostat at first, it stopped heating.

do you think this means anything?

 

[Johntheo5]

I have made an appointment for British Gas to come back but thought I should ask around so I am more knowledgeable about the matter.

So it could be something else causing the high pressure? As the engineer recharged the expansion vessel yesterday afternoon and it was fine after he did that, and it was back to its old tricks again this morning, you have to think that the expansion vessel has gone flat again as it seemed to have solved the problem for about 10 hours.

Unlikely, but possibly one or both filling valves left open. What is the boiler pressure now now and is the system hot or cold and is CH on or off?.

 

[TNDU]

Unlikely, but possibly one or both filling valves left open. What is the boiler pressure now now and is the system hot or cold and is CH on or off?.

it's not possible to leave the filling valve open on this boiler if you mean the filling loop as you have to apply downward presssure on the valve to refill it and when you let that go, it shuts off automatically.

the boiler temperature is currently 58 degrees and the room thermostat is reading 21 degrees, which is the setting on it, so it has reached the desired temprature. The gauge is nearly at 3 again!

 

[dilalio]

Did he drain the boiler before recharging the EV?

 

[TNDU]

Did he drain the boiler before recharging the EV?

I didn't stay in the room but I think he did as I heard water running.

 

[Johntheo5]

it's not possible to leave the filling valve open on this boiler if you mean the filling loop as you have to apply downward presssure on the valve to refill it and when you let that go, it shuts off automatically.

the boiler temperature is currently 58 degrees and the room thermostat is reading 21 degrees, which is the setting on it, so it has reached the desired temprature. The gauge is nearly at 3 again!

What was the pressure this morning when you fired up the boiler?, check it again in the morning before firing the boiler.

 

[TNDU]

What was the pressure this morning when you fired up the boiler?, check it again in the morning before firing the boiler.

The pressure is always fine when the boiler is not on or when it isn't heating from a really cold state. It gets to high when it is heating as fast as it can, so when it is cold.

 

[TNDU]

Unlikely, but possibly one or both filling valves left open. What is the boiler pressure now now and is the system hot or cold and is CH on or off?.

you know what, this was actually the problem! the british gas guy came back and I told him the pressure is even worse than when he left it 5 days ago, despite it continuing to drip water out of the overflow pipe outside.

he said it isn't unusual for the boiler gauge to increase when the boiler is heating at full capacity but i said to him, it shouldn't get above 3 on the pressure gauge and water coming out of the overflow pipe continually when it is heating at full capacity. he then accused me of topping up the pressure myself and i told him i did not touch the damn thing and had called british gas the next day as the problem came back the next day but no one could come until 5 days later.

he then said it may be the infill valve being faulty and letting water back in continually, which would explain why the boiler is still at high pressure when it had a significant amount of water come out of the overflow pipe for the last 5 days and I hadn't touched it. He replaced the filling valve and that seemed to have resolved the problem! so yes, your guess was actually right with regard to the filling valve being left open, but as the valve is auto shut off, it was faulty and didn't close fully.

 

[dilalio]

you know what, this was actually the problem! the british gas guy came back and I told him the pressure is even worse than when he left it 5 days ago, despite it continuing to drip water out of the overflow pipe outside.

he said it isn't unusual for the boiler gauge to increase when the boiler is heating at full capacity but i said to him, it shouldn't get above 3 on the pressure gauge and water coming out of the overflow pipe continually when it is heating at full capacity. he then accused me of topping up the pressure myself and i told him i did not touch the damn thing and had called british gas the next day as the problem came back the next day but no one could come until 5 days later.

he then said it may be the infill valve being faulty and letting water back in continually, which would explain why the boiler is still at high pressure when it had a significant amount of water come out of the overflow pipe for the last 5 days and I hadn't touched it. He replaced the filling valve and that seemed to have resolved the problem! so yes, your guess was actually right with regard to the filling valve being left open, but as the valve is auto shut off, it was faulty and didn't close fully.

On external filling loops, this is why they come with cap ends and the braided hose is meant to be removed when not in use... I was amazed to actually find one in the removed position on a callout at the weekend!

 

[TNDU]

On external filling loops, this is why they come with cap ends and the braided hose is meant to be removed when not in use... I was amazed to actually find one in the removed position on a callout at the weekend!

there is no external filling loop for this boiler. only the one that is in the boiler itself. it has a plastic blue lever that you can pull down to let more water into the system. that filling valve was faulty and didn't shut off properly so it was slowly letting water into the system all the time and the overflow pipe got the excess water out, so it was continually filling and emptying!

 

[dilalio]

there is no external filling loop for this boiler. only the one that is in the boiler itself. it has a plastic blue lever that you can pull down to let more water into the system. that filling valve was faulty and didn't shut off properly so it was slowly letting water into the system all the time and the overflow pipe got the excess water out, so it was continually filling and emptying!

I know it's integral on that boiler... It's bloody useless!
That's why I said "on external filling loops"

I usually cap/put them out of service and use an external replacement - one with a gauge.