Anyone had experience of Repressurising an Expansion Vessel?

[simon1]

Short insight:

Boiler 8 years old (POTTERTON PUMA 80), no previous pressure problems at all.

Last week I punctured one of the CH pipes under the bathroom floor.

Paid plumber to fix pipe (soldered new joint in). Told plumber I'd do the rest.

Plumber advised me to add some inhibiter via the drain outlet of bathroom radiator prior to adding water back to CH system. I could only fit about 1/5 of the bottle into here and had to drain the radiator in room directly below to give enough space to add the rest of the bottle.

Then went to boiler, where I used the filling loop to bring pressure to about 1.5 bar. Switched on CH and all looked OK. One of bedroom radiators was cold, so tried to bleed it - massive amount of air had to be released (a lot more than I've ever experienced). Needless to say, the pressure fell at boiler, so I added more via filling loop.

Now I find the boiler goes from 1.0 cold to over 3.0 hot - and pressure release valve lets water out. I wait for hours for system to cool and get the pressure correct again, but still have same problem.

I look for answers and find an answer //www.diynot.com/forums/viewtopic.php?t=37170 -

4) Repressurising the Pressure Vessel (to the Precharge level)

Try as I might, I can't seem to get things working as described.

I manage to drain enough water to bring pressure down to zero OK, but struggle to get more out. I eventually manage to get the full 10 litres out only by pumping air via the expansion vessel and having both 1x radiator drain valve AND 1x drain valve on the boiler pipework (near to where the filling loop enters).

After releasing the 10 litres of water, I then try to get the expansion pressure vessel to the correct PSi. This is IMPOSSIBLE. It's difficult to do with a footpump, so I used a 12v tyre inflator which has a digital readout. It inflates to 108 PSi in just a few seconds! If I try to inflate to less than this, all of the air seems to escape as soon as I remove the inflator. So I start off high and think I can let air out a bit at a time. After pushing on a 'pencil type' pressure guage just 3 or 4 times to try and messure the pressure, I end up releasing it ALL. I try inflating again and release some air until I've left (at a guess) 30 - 40 Psi.

Now I add water via filling loop to bring the pressure to 1.5 bar on the boilers own pressure guage.

Boiler is working fine now - only rissen by 0.5 bar from cold to hot!

Until..........

Notice some radiators are cold and need bleeding. After bleeding, I'm back to square one - boiler going up and over 3.0 bar!!!!!

Another day, I completely start again from scratch by emptying water/re-pressurising. I now have the boiler pressure running OK, but again have excess air in radiators. So I wait for system to cool, and bleed each rad slowly. As I bleed, I don't allow pressure guage lower than 1.0 bar before adding a little more water first (keeping it between 1.0 - 1.5 bar)

I think I have things sorted, but once again, now radiators are bled, the boiler goes up and over 3.0 bar.

I'm tearing my hair out. Please help

NB The Pressure expansion vessel does NOT leak water when preesing central pin in valve.

 

[Terrywookfit]

Disconnect filling loop to ensure valve is not passing water into system!!!

 

[simon1]

Disconnect filling loop to ensure valve is not passing water into system!!!

Filling loop already disconnected.

Has any one got experience of carrying out the task of re-pressurising?

In particular, how much air (in layman's terms) to put in. Would it be the equivilent of a couple of up/down strokes of a bicycle pump. Afterall, the size of the expansion vessel is only a tea cup.

I can't understand where I'm going wrong. Should I have the drain valve near the boiler or the rad open or closed.

I'm doubting I've got a fault as it's only happened since the accident with the CH pipe last week.

Please help.

 

[billy bob]

You will need a pressure gauge, you cannot guess the pressure simply by up and down strokes of the pump, pump the vessel a few times then check the pressure, there are determining factors for the pressure of the vessel, static head etc, but in a domestic situation you should be ok setting the vessel pressure to 0.2bar below the cold fill pressure, so if your boiler reccommends a 1 bar cold fill pressure of the system, set the vessel to 0.8bar.
Just noticed on your second post, you say that the expansion vessel is no bigger than a cup of tea, that one will not be you heating expansion vessel it is the expansion for the hot water, as the boiler is a combi, there should be a bigger red vessel on the right hand side of the boiler, higher up than the one you are looking at.

 

[ChrisR]

Yep, you've been struggling with the DHW presure vessel not the CH one (see instructions which use those abbreviations)
You access the valve to pump up the CH one over the top of the boiler, at the back. It's about 8 litres!

 

[chrishutt]

Just noticed on your second post, you say that the expansion vessel is no bigger than a cup of tea, that one will not be you heating expansion vessel it is the expansion for the hot water.

Well spotted billy bob. I wish I was half as alert at 5.26 am! What coffee do you use?

 

[simon1]

Doh.....

I've found the CH expansion vessel - Thanks to you guys. I was messing with the wrong one.

The pressure goes up evenly now. Got it to 0.8 bar (manufacturers recomendation). Still have problems with boiler pressure rising past 3.0.

Any more tips?

 

[bengasman]

vessel is dead, not uncommon for these

 

[weareleeds]

It is quite possible that the connection from the expansion vessel to the boiler is blocked & the reason it has started going to 3 bar is before you bled the rad it was acting as an expansion vessel. You can fit a remote vessel anywhere on system but don't just stand it on it's base as you will then not be able to get to the schraeder valve

 

[simon1]

I took out the expansion vessel which was awkward and heavy (full of water). I then undone the flexible pipe............................


Vessel start shooting out water under high pressure and covering me and the garage with manky water I could tell straight away that the pipe was indeed blocked - You couldn't have got an atom down the pipe, nevermind water or air.

It was too late for plumbing merchants, so I ventured to B&Q - but no joy. I'm off in the morning, so I'll try a few 'proper' places for a replacement pipe. I'm going to get new seals for the flue too.

I've pre-charged the vessel to 1.4 bar, so it should be a case of refitting the vessel & new pipe, then filling the CH system with water and inhibitter (sp).

Once I'm done, am I likely to much trouble bleeding excess air from rads?

Thanks to all the posters.

 

[Gasguru]

To avoid getting a soaking, spraying water all over the boiler and looking a prize prat in front of the customer, us pros de-presurise the vessel (via the valve) if there is any suspicion the vessel hose is blocked.

On the Puma the blockage is normally in the formed bend where the flexible hose is swaged. With patience you can some times clear it with a piece of wire. Otherwise get a new hose. Most times though its easier to plumb in an additional vessel (under the boiler for example).

Only presurise the vessel to 0.8 Bar for standard 2 storey property.

Be prepared for the pressure switch to block (or its connection to the diverter), have high resistance on the contacts, also replace the auto air vent - bound to leak or block with all this boiler work.

What new flue seals?

 

[chrishutt]

Firstly you need to precharge the expansion vessel to about 0.8 bar, not 1.4 bar which is too high.

Secondly you should be able to unblock the flexible hose if you manipulate it and then carefully poke through something like the wire from a coat hanger. the connections on the flexible hose might be ¼" or something else unusual so you might find it hard to get a replacement except as the proper spare part.

Thirdly you shouldn't be doing anything with the flue. You should get a competent boiler engineer to do anything with the gas or flue side of the boiler for safety reasons.

 

[ChrisR]

Technique for the blocked hose:
Yes it's usually the red bit. Have known them block absolutely solid.

Get some bicycle brake cable inner (Bowden Cable) eg from Halfords. Cut off about 150mm.
Fold it in two with pliers, making a sharp fold so you have something of a point.
Put the two cut (raggy) ends together (tape helps) into the chuck of a cordless drill/screwdriver.
Push the pointy fold into the end of the blocked hose, and drill slowly.
The cable will go round the bend quite easily and clean it right out.

 

[simon1]

ALL DONE.

I've reduced pressure to 1.2 (in accordance with manufacturers recommendation).

I had to remove the flue in order to access and remove expansion vessel. I've replaced the flue gasket. The boiler is installed in our garage (separate from house) and I have no doubts about the efficiency of the flue since refitting.

I had to drive a 90 mile round trip to find a branch of parts centre with the flexible pipe in stock. £25 for pipe & gasket. Got the inhibiter from B&Q for £13.

Was all set to pay Brit Gas £156 for their set fee repair!

Thanks to this forum and everyone who responded, I've saved over a ton AND had the satisfaction of repairing the boiler myself

 

[billy bob]

The 1.2 bar pressure would be the cold fill pressure of the heating system, the expansion vessel needs to be 0.2bar below this pressure, so 1bar, you need to take a reading of the expansion vessel pressure with the system drained down, otherwise you will get a false reading, if you do not set the expansion vessel pressure correctly you will get problems with the pressure relief valve opening and releasing system water