Central heating boiler losing pressure (again)

Bendy_House

As Bel says, water coming out the plastic condensate pipe is likely to feel a bit warm as it's from the combustion chamber. It will have cooled to a fair degree in the condensate trap, tho', before glugging out the pipe. But being warm doesn't mean it's from a system leak.

That combi boiler has a small analogue pressure gauge? I'm very surprised the boiler doesn't shut down when it gets near zero.

Cool, try the bag test tonight as well. And you are 100% certain there is nothing coming out the copper discharge pipe? 100%

I just did a surf for dyes you can add to the system water to help trace leaks, and the usual type is UV and detected using a UV torch. I did come across a YouTube video with an inspired solution, tho' - add a bottle of cheap perfume to the system water., and go around your house - following your nose - a couple of days later!

Not that I'm recommending it :-:smile:

Bendy_House

And are you up for turning a couple of valves if it comes to it? The boiler is shut off at night - power fully off - and the F&R valves given a quarter-turn to close them. If the pressure still drops, the leak is from within the boiler. 

Granny_98

Last night after switching off the heating I checked the boiler pressure after an hour - boiler pressure was zero, needle at rock bottom. At 10.00am as an experiment, I switched the boiler on without topping up pressure (switched on via room thermostat, which is what I always use to control heating) pressure zero - gurgling and running water sounds heard in boiler and pressure is 1.2 bars 40 minutes later, it reached 1 bar after about 5 minutes, I videod it! All radiators too hot to touch right to the top of each radiator. 

Bendy_House

Granny_98 said:

Last night after switching off the heating I checked the boiler pressure after an hour - boiler pressure was zero, needle at rock bottom. At 10.00am as an experiment, I switched the boiler on without topping up pressure (switched on via room thermostat, which is what I always use to control heating) pressure zero - gurgling and running water sounds heard in boiler and pressure is 1.2 bars 40 minutes later, it reached 1 bar after about 5 minutes, I videod it! All radiators too hot to touch right to the top of each radiator. 

Weirder and weirder.

I'm surprised the boiler still fires up when showing zero pressure. Mind you, that reading is from the analogue gauge, yes? Whereas the boiler will be monitoring the pressure via an internal sensor. Having said that, the internal sensor mush also surely be reading zero, or close to it?!

Anyhoo, after the boiler fired up, the pressure rose quickly to 1.0bar. That will almost certainly be due to the system water being heated, so it expands. Obviously the EV should be accommodating this increased volume - that's its job - but the fact it isn't does suggest your EV is still faulty.

I don't suppose you had the bag tied over the copper discharge pipe last night when the boiler lost pressure? Ah, shame...

MouldyOldDough

We have a 15 year old Worcester boiler that kept losing pressure and eventually this was sorted by fitting an external expansion vessel - it is a large red bulb that needs connecting to the heating circuit !

https://www.wolseley.co.uk/product/center-(cb)-domestic-heating-expansion-vessel---25-litre/

Granny_98

Bendy_House said:

Weirder and weirder.

I'm surprised the boiler still fires up when showing zero pressure. Mind you, that reading is from the analogue gauge, yes? Whereas the boiler will be monitoring the pressure via an internal sensor. Having said that, the internal sensor mush also surely be reading zero, or close to it?!

Anyhoo, after the boiler fired up, the pressure rose quickly to 1.0bar. That will almost certainly be due to the system water being heated, so it expands. Obviously the EV should be accommodating this increased volume - that's its job - but the fact it isn't does suggest your EV is still faulty.

I don't suppose you had the bag tied over the copper discharge pipe last night when the boiler lost pressure? Ah, shame...

There's a bag been tied on the copper pipe all the time, not a drop of water in it - also got the condensate pipe end in a jug to monitor output! About 100ml in it this morning while heating was off 

Granny_98

MouldyOldDough said:

We have a 15 year old Worcester boiler that kept losing pressure and eventually this was sorted by fitting an external expansion vessel - it is a large red bulb that needs connecting to the heating circuit !

https://www.wolseley.co.uk/product/center-(cb)-domestic-heating-expansion-vessel---25-litre/

My boiler is still under warranty as it's only 5 years old, it replaced an almost 15 year old boiler with the same problem! But thank you for the suggestion x

NSG666

Granny_98 said:

5 year old gas CH boiler, serviced December - boiler had been losing pressure - installers rang manufacturer - sent out engineer, who reinflated expansion tank. Installers rang them and saud it need a new expansion tank, a week later called back, supposedly fitted a new expansion tank ( wasn't here as long as first visit) 5 weeks later, boiler losing pressure again. (engineer said if it loses pressure again I've got a leak) boiler requires filling about twice a day, sometimes, if I'm sitting next to it, there is an audible "gulp" as pressure is lost. Boiler has a 10 year warranty, Is it still the expansion tank? I don't turn my heating off in the winter, just turn it down 21°C during the day and 18°C at night as I can't stand being cold (pensioner) 

Unless there is the right access (rare) it's not possible to replace the expansion vessel in that WB boiler without removing the boiler entirely from the wall. Not a quick job which is why the replacements are usually put external to the boiler.

Given the 5 week time lag it seems that the expansion vessel was merely repressurised and it then lost it's pressure over the following 5 weeks. From then on every time the boiler heats up it (the heating system) over-pressurises and forces water out of the safety valve. Pressure drops, you top up, repeat....

It sounds like you use the original installer for servicing so call them about the problem and see what they say/suggest. If it is the expansion vessel or boiler that's at fault you don't want to be paying but if it is a leak then it needs finding and sorting.

Bendy_House

Granny_98 said:

Bendy_House said:

Weirder and weirder.

I'm surprised the boiler still fires up when showing zero pressure. Mind you, that reading is from the analogue gauge, yes? Whereas the boiler will be monitoring the pressure via an internal sensor. Having said that, the internal sensor mush also surely be reading zero, or close to it?!

Anyhoo, after the boiler fired up, the pressure rose quickly to 1.0bar. That will almost certainly be due to the system water being heated, so it expands. Obviously the EV should be accommodating this increased volume - that's its job - but the fact it isn't does suggest your EV is still faulty.

I don't suppose you had the bag tied over the copper discharge pipe last night when the boiler lost pressure? Ah, shame...

There's a bag been tied on the copper pipe all the time, not a drop of water in it - also got the condensate pipe end in a jug to monitor output! About 100ml in it this morning while heating was off 

My apologies for doubting you :-)

I'm afraid I'm out of ideas. Can you keep us updated please - it's a strange one.

Granny_98

NSG666 said:

Unless there is the right access (rare) it's not possible to replace the expansion vessel in that WB boiler without removing the boiler entirely from the wall. Not a quick job which is why the replacements are usually put external to the boiler.

Given the 5 week time lag it seems that the expansion vessel was merely repressurised and it then lost it's pressure over the following 5 weeks. From then on every time the boiler heats up it (the heating system) over-pressurises and forces water out of the safety valve. Pressure drops, you top up, repeat....

It sounds like you use the original installer for servicing so call them about the problem and see what they say/suggest. If it is the expansion vessel or boiler that's at fault you don't want to be paying but if it is a leak then it needs finding and sorting.

Expansion vessel was repressurised on the first visit, he was here approx two hours 2nd visit, and the pdf I received after 2nd visit says EV was replaced. There is atleast 60cm height above the boiler if the flue is removed as it is a tall room, though engineer did say about the boiler needing to be removed on first visit. Engineer refused to wear a mask so I stayed in another room and didn't witness his work