Expansion vessel pressure & silicone grease inside dust cap?

[kevkdg]

Hi,

Query on expansion vessel pressure readings...

Chap came out due to a boiler fault (Vokera Compact 24), and decided to check the expansion vessel pressure. He couldn't figure out how to drain the boiler pressure locally so went on a hunt for a drain point on a radiator, which there wasn't any. In the past I'm sure engineers have isolated the boiler by closing the flow and return valves and dropped the boiler pressure. He did neither and just connected a pump to the schrader valve to get a reading. He said it was 1 bar... BUT can this be an accurate reading without isolating the boiler and dropping the pressure?

Also, when he finished he filled the schrader valve dust cap with "Silicone Grease". Never seen that done before and am unsure why he did this, I am thinking that would have just clogged up the valve and any dirt etc would just stick to it.

 

[flameport]

The pressure indicated would just be the pressure of the complete system. Doesn't mean anything else - the expansion vessel could be full of air, full of water or some combination of those.

Grease is not required and serves no purpose.

 

[kevkdg]

The pressure indicated would just be the pressure of the complete system. Doesn't mean anything else - the expansion vessel could be full of air, full of water or some combination of those.

Grease is not required and serves no purpose.

Thanks, I thought the same about the grease, now how to get it out of the valve, it's not easy to access it and I don't want to press the valve as it will let air out....

 

[kevkdg]

Also, does anyone know how to drain the Vokera Compact 24? The chap had a go at trying to remove the Pressure Release Valve with some water pump pliers hence the scuff marks on it, not really sure what he was trying to do, especially as he hadn't isolated the flow and return either! What is the transparent plastic tube connected to? Doesn't seem to be labelled in my boiler schematic? But it looks like it could be a drain valve?

 

[Harry Bloomfield]

The chap had a go at trying to remove the Pressure Release Valve with some water pump pliers hence the scuff marks on it, not really sure what he was trying to do, especially as he hadn't isolated the flow and return either!

Looking at the PRV, it needs a particular type of C spanner to undo it, reading your other comments, I would suggest not inviting the clown back.

You can undo the core of the Schrader valve, with a key made for the job, from any car accessory shop. Removing it, should bring most of the grease out with it. After cleaning and refitting, you can restore the pressure with a car or a bike pump, though I doubt the grease will do any harm. .

 

[ianmcd]

It is a good idea to put silicon grease onto the schraeder valve before pumping the vessel up, it lubricates the O ring on the schraeder core and stops it letting by , but the EV pressure can only be cheched and charged with the boiler de-pressurised and a drain point left open while pressurising, in your pic the plastic hose IS the boiler drain point

 

[kevkdg]

It is a good idea to put silicon grease onto the schraeder valve before pumping the vessel up, it lubricates the O ring on the schraeder core and stops it letting by , but the EV pressure can only be cheched and charged with the boiler de-pressurised and a drain point left open while pressurising, in your pic the plastic hose IS the boiler drain point

Thanks @ianmcd

I assume these are the flow and return valves I need to close using a screwdriver prior to draining the boiler pressure before checking the EV pressure.

 

[ianmcd]

Thanks @ianmcd

I assume these are the flow and return valves I need to close using a screwdriver prior to draining the boiler pressure before checking the EV pressure.

View attachment 295684

I wouldnt close them, they will probably leak when you open them again, open the drain valve and when the water stops running leave the drain point open and then start pressurising the vessel, more water will probably start coming out, once this stops then you are pressurising the vessel, take it up to 0.8 Bar slightly higher if you want as some pressure will escape when you remove the pump from the schraeder but dont add too much pressure

 

[Johntheo5]

It is a good idea to put silicon grease onto the schraeder valve before pumping the vessel up, it lubricates the O ring on the schraeder core and stops it letting by , but the EV pressure can only be cheched and charged with the boiler de-pressurised and a drain point left open while pressurising, in your pic the plastic hose IS the boiler drain point

I had never heard of this silicon grease idea but I see some schrader type bicycle tyre/tubes (after removing the dust cap!) have a nut attached to the valve stem that must be loosened before the tyre can be pumped up, you then retighten it afterwards. My old ex postman's Rudge with its parcel carrier on the front certainly didn't have this, you could get valve rubber tubing.

 

[Harry Bloomfield]

My old ex postman's Rudge with its parcel carrier on the front certainly didn't have this, you could get valve rubber tubing.

That was a slightly different type of valve, to the Schrader. As a valve - It used a simple, thin metal tube, stopped off at the end, with a couple of tiny holes at the side. The rubber tube was a tight fit, over the tube, so it acted as a one way valve.

 

[Johntheo5]

It still seems to be for sale IF this is it, seems enough here to service hundreds of valves.

 

[Harry Bloomfield]

You always got a short piece of that, with a bike puncture outfit.

 

[kevkdg]

I wouldnt close them, they will probably leak when you open them again, open the drain valve and when the water stops running leave the drain point open and then start pressurising the vessel, more water will probably start coming out, once this stops then you are pressurising the vessel, take it up to 0.8 Bar slightly higher if you want as some pressure will escape when you remove the pump from the schraeder but dont add too much pressure

@ianmcd thanks for the tips. Looks like I have a faulty heat exchanger, as the pressure still rises even after checking the expansion vessel correctly. If the tap supplying the mains feed to the hot water side is closed off, the pressure stabilises and the pressure relief valve closes. However, the insurance company won't repair it as the engineer said the flu needs replacing which is not covered and needs resolving first. It has corroded on the end on the external inner pipe which I think must be due to weather exposure. Struggling to get anyone to quote on replacing. I'm not convinced it is particularly unsafe as it's outside anyway. Guard removed to take photo.

 

[ianmcd]

Yes unfortunately that is indeed classed as unsafe, but you can still buy a replacement flue for it, not a huge job to replace

Vokera Standard Efficiency Horizontal Flue

Vokera SE Horizontal Flue

www.mrcentralheating.co.uk