Vaillant ECOtec PLUS lost pressure: reason: a faulty Schrader Valve!

Annemos

I had the annual service this afternoon. 8 year old Boiler.

He went away. Within half an hour, the pressure had gone from 1.8 to 0.0.  Safety cut-out kicked in, due to water pressure being too low.

(Me having visions of burst pipes etc etc. Called them back in a panic!)

The chap has just come back, thank goodness. It turned out to be a clogged up Schrader Valve.

This is a tiny little thing about an inch long. And apparently it works like a car tyre and pumps air in. 

I thought this might be useful information for people. He replaced it in 5 minutes. 

daveyjp

He may have been fiddling with the valve during the service if he repressurised the expansion vessel.

Annemos

Yes, it was his brother who came back and said that his brother had been doing something around that big vertical metal box thing on the top right. (Is that the expansion vessel? )

He showed me the old valve and it was quite black on one end. 

Luckily this brother was on the way to a Fish and Chip shop near me, so was near enough to call in. I was so grateful, I paid for his and his wife's fish and chips! 

ThisIsWeird

Good result! And also good to hear that checking on the EV was done as part of the service - I suspect often neglected.
Yes, the EV is a bulbous cannister, often coloured a dull red.
Fish 'n' chips, mmmmmmm.

Annemos

That will be it. But this one, from memory, is a very smart looking steel one. About 30cm high and 25cm wide? And there is a black button in the middle of it. That button contained the offending Schrader Valve. 

Amazing that such a small thing, could stop the boiler functioning. They said something like..."if it is gunged up or if the bit inside does not go back exactly into the middle, then it can fail to operate.

(That reminded me of my press-button loo valve that likes to fail rather often!) 

They said it happens on many of these boilers eventually, although some do get away with not ever having to replace it. 

Eldi_Dos

 In some parts of the world traffic cops carry a Schrader valve key and use them to remove valves from illegally parked cars, saves on paperwork and seems to be quite effective.

ThisIsWeird

Annemos said:

That will be it. But this one, from memory, is a very smart looking steel one. About 30cm high and 25cm wide? And there is a black button in the middle of it. That button contained the offending Schrader Valve. 

Amazing that such a small thing, could stop the boiler functioning. They said something like..."if it is gunged up or if the bit inside does not go back exactly into the middle, then it can fail to operate.

(That reminded me of my press-button loo valve that likes to fail rather often!) 

They said it happens on many of these boilers eventually, although some do get away with not ever having to replace it. 

Ah yes - yours is a nice metallic silver... :-(

That 'button' is a safety cap, just like the ones on your car tyres.

Inside that vessel is a flexible rubber diaphragm that splits the vessel in two. On one side is the system water - the boiler, radiators, that sort of stuff. On the other is air, which needs to be pressurised to a certain level, usually around 0.5 bar, so that it retains an air volume inside the vessel. This is pressurised via that Schrad valve.

Hot water expands, so when your boiler heats up, all that expansion needs to go somewhere. It goes into this vessel, pushing the diaphragm against the compressed air, and keeping your system pressure constant and happy. When it cools down again, the air side 'pushes' the water back out.

If the air side doesn't have any pressure in it, the water side will have already filled the air side even when cold, pushing that dia tight against the vessel wall. When your system then heats up, the expanded water has nowhere extra to go = huge pressure increase and popping valves...

Annemos

ThisIsWierd   Could this affair have done any actual lasting damage to my boiler? 

Or would the safety cut out at about 0.3 with Code 22, have prevented any real damage? 

Thank you so much for your time and attention. I really appreciate it. 

(Your description of what happens is very impressive.) 

It makes one think... the world is run by valves... heart valves etc. 

ThisIsWeird

No lasting damage.
A discharged EV will usually cause the pressure to soar when the boiler heats up, since the expanded water has nowhere to go. When this pressure reaches the allowed safety max of 3bar, a safety valve (yup, another valve...) blows open and the excess hot water is discharged safely outside the house - look for a 15mm copper pipe on the wall outside where the boiler is located. 
This prevents anything blowing up!
A not uncommon issue following this is that the safety valve sometimes doesn't reseal properly, so continues to let-by even after the EV is fixed.
When the opposite happens - the system pressure drops excessively such as to your 0.3bar, the boiler should just shut down and not work.
Both are situations that most folk will experience at some point in their happy lives with their boiler.

Annemos

Yes, with mine, no water at all came out of the outside pipe. Just the pressure dived downwards. 

Thank you very much again for all the explanation.

(I do slightly feel that I have a potential bomb in the house!) 

ThisIsWeird

Annemos said:

Yes, with mine, no water at all came out of the outside pipe. Just the pressure dived downwards. 

Thank you very much again for all the explanation.

(I do slightly feel that I have a potential bomb in the house!) 

Usually, if an EV fails, or has lost its air, the symptoms will be a rising pressure, followed by a drop if the safety valve has been popped, and water lost.
Yours didn't get that far :-)
In yours, the Schrader leaked and released the air, so system-water filled the EV instead. That caused the pressure drop.
Had you responded by topping up the pressure, then you'd have a vicious cycle of rising pressures, and drops!
No 'bomb'. I mean, when was the last time a boiler blew a house up? 
Um, ok, the time before that? Ah, fair do's - bludy scary :-)
No worries - all these explosions are down to leaking gas, not a failed EV :-)
(And, very likely down to folk tampering with their gas meters...)