Central heating boiler losing pressure (again)

Granny_98

[Deleted User] said:

If your boiler has a 10 year warranty and it has been serviced regularly then I would be asking WB to resolve the issue. They have their own team of engineers and they carry most parts on the van. I called them out to my boiler last year and they happily replaced the fan and the syphon. The service visit cost me nothing. 

And their engineer said if it lost pressure again it's not the expansion vessel, a more obnoxious man would be hard to find. I will specifically ask that this engineer does not attend if I can. However I am not 100% sure that it is not leaking under the floor from the radiator pipework

Bendy_House

If you can do that isolating test, Granny, then great. Obviously, boiler fully turned off at t'leccy mains.

I totally get where you are coming from. Your boiler is under warranty, but you have some concerns about the quality of engineer being sent out, and what they might be saying. Tbh, tho', as long as they are 'competent' and actually fix the darned thing, it doesn't matter too much if they are obnoxious - you ain't going out for a pint with them :-)

(Once the issue is sorted, tho', no harm in dropping the CO an email about 'customer relations', citing accurately your experience...)

You clearly have a good grasp of what's going on, and just want to be 'informed' so you can deal with unknowns and, especially, BS. That is absolutely fair do's in my book.

NSG666

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. 

Can you reverse this experiment i.e. set the pressure to 1bar when the system is cold, turn the heating on and see what the pressure gauge goes up to at say 10 min intervals?

Also, with the system cold, go round all of the radiator valves and give the joints a good wipe with loo roll (better still some coloured tissue if you have some as it goes dark as soon as it gets wet). Check the tissue after each valve to check it's dry and do it when cold as it's often easier to detect a leak when cold.

It's not impossible that one of the push-fit fittings has worked off a bit and started to leak if it was not pushed home fully at installation even if that was 20 years ago.
At least it sounds like any potential leak will be under the ground floor or you would have seen water staining on the ceiling by now.

Granny_98

Bendy_House said:

I have read (on here) about certain WB boilers having their EV's located at the back of the boiler, 

Mind you, isn't lifting off and replacing a boiler a 2-person job? In which case, did this person actually replace the EV as claimed?

The pressure has never soared on either of my boilers, the EV is indeed at the back of the boiler, I have taken a few photos as I can't see it even standing on steps - I part watched a you tube video - the EV of mine is square/rectangular silver colour (not red/round like the one I watched on you tube) with a black screw cap (valve?) the flue is screwed onto the boiler and the flue exit is screwed also (for 90° bend) with a collar to flue on inside and outside wall
As to whether the EV was replaced, the engineer worked alone, the paperwork says it was, do I believe that............ 

Granny_98

NSG666 said:

Can you reverse this experiment i.e. set the pressure to 1bar when the system is cold, turn the heating on and see what the pressure gauge goes up to at say 10 min intervals?

Also, with the system cold, go round all of the radiator valves and give the joints a good wipe with loo roll (better still some coloured tissue if you have some as it goes dark as soon as it gets wet). Check the tissue after each valve to check it's dry and do it when cold as it's often easier to detect a leak when cold.

It's not impossible that one of the push-fit fittings has worked off a bit and started to leak if it was not pushed home fully at installation even if that was 20 years ago.
At least it sounds like any potential leak will be under the ground floor or you would have seen water staining on the ceiling by now.

The boiler has never been above 1.5 bars. I have checked the radiators for leaks previously though possibly not when cold, which I will do tonight ir tomorrow morning, however, apart from bathroom and kitchen home is carpeted and I dont have any wet carpet, if there is a leak it will be under the floor pipework. I do have a railway line behind my home, and my brother has suggested rodents could have chewed through the plastic pipes, but if my dog had heard anything at all she would have barked continuously! I don't have any pipes above the ground floor, so no ceiling leaks (bungalow) even my toilet overflow is waist height! Although I have been switching heating on and off the last week - I would normally have the heating on 24/7 as the comfort level far outweighed the cost (only 10% more pre price increase which I suppose will still be 10% more post price increase!) but I'm worried about that with these problems I have been having

NSG666

Granny_98 said:

NSG666 said:

Can you reverse this experiment i.e. set the pressure to 1bar when the system is cold, turn the heating on and see what the pressure gauge goes up to at say 10 min intervals?

Also, with the system cold, go round all of the radiator valves and give the joints a good wipe with loo roll (better still some coloured tissue if you have some as it goes dark as soon as it gets wet). Check the tissue after each valve to check it's dry and do it when cold as it's often easier to detect a leak when cold.

It's not impossible that one of the push-fit fittings has worked off a bit and started to leak if it was not pushed home fully at installation even if that was 20 years ago.
At least it sounds like any potential leak will be under the ground floor or you would have seen water staining on the ceiling by now.

The boiler has never been above 1.5 bars. I have checked the radiators for leaks previously though possibly not when cold, which I will do tonight ir tomorrow morning, however, apart from bathroom and kitchen home is carpeted and I dont have any wet carpet, if there is a leak it will be under the floor pipework. I do have a railway line behind my home, and my brother has suggested rodents could have chewed through the plastic pipes, but if my dog had heard anything at all she would have barked continuously! I don't have any pipes above the ground floor, so no ceiling leaks (bungalow) even my toilet overflow is waist height! Although I have been switching heating on and off the last week - I would normally have the heating on 24/7 as the comfort level far outweighed the cost (only 10% more pre price increase which I suppose will still be 10% more post price increase!) but I'm worried about that with these problems I have been having

That's interesting as the pressure going up to c3.5bar is usually the main sign that there is a problem with the expansion vessel so I'm not sure why it has been replaced unless it was mis-diagnosed.

Anyway, regardless of that, it was only the way you phrased your 1st post that cast doubt on whether the EV had been replaced but nothing else you have said since indicates it hasn't nor needed to be.

I'm sure your engineer will be able to isolate the boiler then crank the pressure up in the radiator circuit to either blow the dodgy fitting apart or make it easier to see water spraying out somewhere. Unfortunately it will be trial and error accessing the right spot under the floor.

Bendy_House

Ooh, just had a thought that could fit in with your symptoms.

You understand what's inside an EV? It's divided in two by a flexible rubber diaphragm inside. One side is connected to the system water, and the other is compressed air - that's why it has the 'car valve' on it.

The idea is that the air side is charged to around 1 bar, which clearly expands the R-D all the way to the water side. When you then pressurise the water side, system water will go in to the EV and push the RD to roughly half-way.

You then fire up your boiler and the system water expands - this excess water forces itself into the EV and pushes further against the air side, and this keeps the pressure pretty constant. When the system cools, the water contracts and leaves the EV again.

When an EV fails, it's usually because the RD tears or becomes pin-holed. What happens if it's pin-holed? Air will seep out and enter the water side, and the RD will slowly collapse. When the air side is near empty, the EV will no longer work and the system pressure will start to soar when it heats up, and will 'blow' the discharge valve if it reaches ~3bar.

Ok, I wonder if your EV is at the early stages of this? What will happen is, air will seep out, form a large bubble inside the EV on the water side until it then passes into the main system water either because the bubble is large enough, or perhaps it's when the system is cooling down. This could well make the 'glug' you've heard!

Then what? This air is automatically expelled from the system water by the auto-air-vent in your boiler = pressure drop.

If this is what's happening, then what you will find is that over the next week or so, your system pressure will start to climb as the heating goes on. Ie, when enough air has been lost for the EV to work. And, when ~3 bar is reached, water will be expelled out the discharge pipe.

in_my_wellies

Bendy-House
Many thanks for your detailed description. You have been so helpful to the OP. Thank you! And very interesting 

I had problem with pressure in my BAXI boiler. The engineer said probably the EV but could be another part. He replaced the EV tank but it didn't fix it so came again and replaced the other part. That fixed it. I don't know the name of that but it was relatively cheap (£12?) and I wished he had replaced both in the one visit to save me another £75 call out charge. Fully appreciated it was a good idea to change the EV as it over 17 yrs old. But in one visit! 

Granny_98

I switched the heating off, left it a while (2 hours) the pressure dropped (but not to zero) refilled to 1 bar, turned heating & hot water down to minimum then isolated the boiler. Got up at 7.30 & it was all as I left it, as I was about to undo the isolation I decided to video it and had my phone on a stand fixed to reading the dials on the boiler, reversed the isolation and fully expected  the pressure to drop etc if the fault was in the pipework - and nothing happened! I kept videoing in 5 & 10 minute slots (what's that saying "a watched pot never boils" so true!) & nothing. Bendy_house - My plumber sticks a pressure gauge into that black valve, which is why he said it needed replacing in December, so I will phone him Monday if this continues. 

Granny_98

in_my_wellies said:

Bendy-House
Many thanks for your detailed description. You have been so helpful to the OP. Thank you! And very interesting 

I had problem with pressure in my BAXI boiler. The engineer said probably the EV but could be another part. He replaced the EV tank but it didn't fix it so came again and replaced the other part. That fixed it. I don't know the name of that but it was relatively cheap (£12?) and I wished he had replaced both in the one visit to save me another £75 call out charge. Fully appreciated it was a good idea to change the EV as it over 17 yrs old. But in one visit! 

Can't you find your bills and have a look LOL!