Replace 10 litre expansion vessel. DIY job?

[Furnace]

It appears that the expansion vessel has failed. Water comes out of the schrader valve for a few seconds, then air. Leaving it for a few seconds, the same thing happens again. This suggests that there is a hole in the diaphragm? I've ordered a direct replacement.
Is it a simple DIY job to replace it?
I was intending to:

1. Turn off the mains and open a hot water to depressurise the system.
2. Unmount the expansion vessel and move it outwards from the boiler to the extent of the braided hose.
3. Position it over a bucket
4. Undo the fitting on the old EV base.
5. Pray water doesn't piss everywhere.
6. Install flexible fitting on base of new EV.
7. Check pressure on EV with tyre pressure gauge
8. Remount EV on boiler.
9. Turn on mains water.
10. Pray

Does that sound reasonable? What have I missed

 

[ProDave]

That's a system boiler not a combi, so opening the hot tap won't let off the pressure.  That EV is for the sealed heating system.

 

The water should already be turned off. There is an over pressure release valve on the top of the boiler if you remove the top cover, you can manually open that to let off the pressure. But the pressure already looks very low.

[Furnace]

Thanks Dave.

I should replace 1. with "Remove boiler cover and release any excess pressure from the system"
and 9. with "repressurise boiler system by opening filling loop valve"

Makes sense?

 

[Temp]

I think you should drain the heating system not just release the pressure. Unless there is a way to isolate the expansion vessel from the rads. If it needs draining put corrosion inhibitor back in afterwards (eg Fernox f1 or similar). What does @Prodave think?

 

May need ptfe tape for the connection to the expansion vessel.

 

 

Edited January 15, 2023 by Temp

[PeterW]

@Furnace from memory those hoses have a rubber washer in them on the face of the joint with the expansion vessel. Ideally you want to change that too, or at least turn it over and re-seat the hose.

 

Good opportunity to drain and refill with inhibitor as @Temp said - when was the system flushed last ..??

 

 

[Furnace]

The system is about 15yrs old (installed as part of a new build) and is "serviced" every couple of years, although I've not been there when it's been done as my folks live there. There are no radiators and it serves the underfloor heating system. I don't know if it has been, or needs to be, drained and inhibitor renewed?

 

[Temp]

There is servicing and servicing.

 

The big companies that take a monthly fee almost never flush a system or check/change the corrosion inhibitor, they just service the boiler. They frequently claim they aren't allowed to go in the loft to tip inhibitor into the header tank on a ventilated rad system but it can be added via a rad bleed valve. Over time corrosion create sludge and then one autumn you turn it on for the first time in ages and you find some rads don't heat up. They rock up and either get the sludge moving or tell you you need a power flush cost £300 - £900. Some CH pumps even stir the system occasionally to try and prevent the sludge settling out in the summer but that's only going to delay problems.

 

This is less of an issue with UFH as there are fewer metal parts to corrode but I still like to keep my system inhibitor at the right level. The thought of a blocked UFH pipe gives me the shivers.

 

You can buy a corrosion inhibitor test kit for around £10 to see if there is any left in the system. 

 

If you need to add some its worth estimating the volume of water in the system when you drain it so you get the concentration right. Our system needs several bottles if F1. They say putting in too much isn't a problem though apart from the cost.

 

[Furnace]

52 minutes ago, Temp said:

You can buy a corrosion inhibitor test kit for around £10 to see if there is any left in the system

Thanks for that. I'll get one of those kits to determine if it needs more inhibitor.

[Furnace]

If it does need more inhibitor, what's the best way to add it? I've previously only ever added it to an unvented expansion tank when refilling the circuit.

M

[Furnace]

Job done and it looks to be running at the correct pressure now. It's too cold to mess around with draining down and refilling - it's my folks' house and they're in their 90s.

Thanks to all for input and saving me waiting 2 weeks for the next available plumber.

It looks like there may have been a micro-weep around the EV vessel causing corrosion. I've put on PTFE tape that may (or may not) prevent it happening again. It's 15yrs old, so I'm not too miffed.

[Furnace]

Final question for the panel...

The isolating valve for the filling loop circled in blue has a weep emanating from the valve actuating shaft that keys on to the black handle. I've positioned it so that there is currently no leak, but I'd prefer to replace it so there's peace of mind. Is there a particular type that is required because it's in a hostile, high temperature environment? The supplied Grant version is about £20 which appears a bit steep?
I'll need to drain down the system in order to replace it.😔
 

[PeterW]

Weep will probably disappear when the boiler is properly back to temperature as it’s screwed into the iron tee on the tank. You “can” change them but they are a b#tch to align and are usually put in with Jet Blue or similar so they don’t need to bed down to create a seal. 

[Furnace]

10 hours ago, PeterW said:

Weep will probably disappear when the boiler is properly back to temperature as it’s screwed into the iron tee on the tank. You “can” change them but they are a b#tch to align and are usually put in with Jet Blue or similar so they don’t need to bed down to create a seal. 

Thanks so much Peter. I don't fancy wrestling the old one out, nor aligning the new one so I'll keep an eye on any weeping but leave it be for the moment. Thankfully the EV change has resolved the heating issue and my elderly parents are now reclining at 21degC rather than 16.

Thanks to all who contributed

Mark