Plumbing problem...

[John Brown]

I decided that the expansion vessel on my CH system could use a bit of pumping, as the water pressure in the system swings wildly from not much to a lot as the temperature increases. Attached the pump - nothing - can't get any air in. Tried pressing the pin on the Schrader valve - solid. Can this be because there's no air in there, or is it more likely to be a stuck valve?
By the way, I know that I should let some water out and relieve the pressure, but I don't want to get too involved with this until the weather improves...

 

[duke]

I decided that the expansion vessel on my CH system could use a bit of pumping, as the water pressure in the system swings wildly from not much to a lot as the temperature increases. Attached the pump - nothing - can't get any air in. Tried pressing the pin on the Schrader valve - solid. Can this be because there's no air in there, or is it more likely to be a stuck valve?
By the way, I know that I should let some water out and relieve the pressure, but I don't want to get too involved with this until the weather improves

Don't blame you, friend had an issue with his, luckily he had an isolation valve before it and changed it out. There was a lot of calcium build up around valve.

 

[duke]

His water supply is from a well, ours is too and we have a softner system which keeps it at bay. Otherwise our dishwasher would only last a few years. We are on well water also.

 

[Fitzroy]

Suggests to me that the vessel has failed. I removed a vessel earlier this year with the same behavior. I used a high pressure mountain bike suspension pump to force the valve open after that any air put in leaked past the diaphragm.

 

[ChaiLatte]

How much pressure is in the system?

Is it a bog-standard Schraeder valve? If so, buy a valve removal tool (e.g. from Halfords) or even a metal valve dustcap with the top slotted and unscrew the valve a little. What escapes (air, water, both) will tell you if there is pressure in there. Buy a spare valve at the same time as the tool and swap them out quickly.

 

[Pedronicus]

Buy a spare valve at the same time as the tool and swap them out quickly.

VERY QUICKLY if system still under pressure and have a few cores within reach in case you drop one! Don't ask how I know this!

 

[ChaiLatte]

VERY QUICKLY if system still under pressure

Tyre fitters do not seem to have too much problem doing this when they seat the bead with no core in the valve, remove the air and screw the valve in. Is the pressure in a tyre in the same field as that in a heating system?

 

[Pedronicus]

Tyre fitters do not seem to have too much problem doing this when they seat the bead with no core in the valve, remove the air and screw the valve in. Is the pressure in a tyre in the same field as that in a heating system?

Air from a tyre is slightly less messy that water which will be expelled if the diaphragm inside the pressure vessel has failed and the system pressure has not been dropped. The off load standing pressure in a heating expansion vessel can be between 1.5 to 3 Bar.

 

[ChaiLatte]

Air from a tyre is slightly less messy that water which will be expelled if the diaphragm inside the pressure vessel has failed

If water comes out when he first cracks the valve, indicating diaphragm failure, why would he proceed to change the valve?

A speedy change of a stuck valve in a good system just saves you a bit of pumping (if you can screw the valve in with 10psi still in the system, that means your arm does not have to reinsert that same 10psi).

 

[John Brown]

I have spare valves and the removal tool, so will maybe try the "loosen it a little" thing.

 

[Fergie 307]

Your boiler will probably have inbuilt isolation valves, so isolate it from the rest of the system first. If water comes out of the valve then you will need a new expansion vessel. Can be a relatively easy DIY job, depending on the design.

 

[John Brown]

I'll take a closer look, see if I can find an isolator valve. It's a horrible installation, giant water tank with bad access to pipework behind it.

 

[Yorkieguy]

This might help a bit:

https://www.google.com/search?q=do+...e=ive&vld=cid:4f8d3fe0,vid:7-ljKqnIo9U,st:198

 

[Fergie 307]

I'll take a closer look, see if I can find an isolator valve. It's a horrible installation, giant water tank with bad access to pipework behind it.

The boiler will generally have its own valves built into the tails before they leave the bottom of the unit. No real reason for the air valve on the expansion vessel to stick apart from corrosion. All that should be around it is air so if it is solid I am guessing it is because the diaphragm has failed, allowing water into the air side of the chamber and corroding it up. All will be revealed once you get it out !

 

[John Brown]

The boiler will generally have its own valves built into the tails before they leave the bottom of the unit. No real reason for the air valve on the expansion vessel to stick apart from corrosion. All that should be around it is air so if it is solid I am guessing it is because the diaphragm has failed, allowing water into the air side of the chamber and corroding it up. All will be revealed once you get it out !

I should have mentioned that this is an external expansion vessel, so I'm not sure the boiler tails will help with isolation.

 

[Pedronicus]

I should have mentioned that this is an external expansion vessel, so I'm not sure the boiler tails will help with isolation.

In that case you will have to drop the pressure off the whole system by using a system draincock. If there is water from the schrader valve on the vessel then it will need to be replaced. If not then you will probably have to re-pressurise the vessel to the required level (pre-charge pressure should be shown on the vessel somewhere) and then top up the system in that order.

 

[Spectric]

Is this a combi system or a system boiler with remote expansion vessel ? If the expansion vessel diaphragm has failed and you have re-pressurised the system then once the water temperature increases then the over pressure valve will be letting water out, is this the case ?

 

[John Brown]

It's a Frankenstein boiler. Vaillant Eco Max combi, but the hot water side blanked off, so it's running as a system boiler. This was probably because the house has solar water heating as well. It's not ideal, as it means you can't set different temperatures for the CH and the HW, but it is what it is. It actually has two expansion vessels, one for the boiler and one for the solar panel loop.
Currently, the pressure in the main CH/tank coil is at the bare minimum, as it does indeed dump via the overpressure valve if topped up. I don't really want to get into anything too major right now, as I'm hoping to drain down and change a few sticky thermostatic valves if summer arrives. Maybe have to use an upstairs radiator as an expansion vessel for a while.
P.S. I don't know if the expansion vessel has failed or not, all I know is that the Schrader valve is stuck...

 

[Fergie 307]

So if you top it up to normal working pressure, let's say 1bar, then run the heating, when it gets warm it dumps water from the over pressure valve?
This sounds very much as though the diaphragm has gone in the expansion vessel. If that is the case then you will have water behind your Schrader valve at system pressure. To avoid a right old mess I would depressurise the system before trying to remove it.

 

[sploo]

This thread is interesting, because we have a mains pressure hot water system that kills expansion vessels like they're going out of fashion. We're on our third in seven years, and that one's failed too