Swiftflow 75 pressure prob - advice gratefully received

[R6Rich]

Hi Guys,

Spent a lot of time reading through this forum and haven't found the answer to my problem yet, so I really hope some of you very helpful chaps can offer some advice.

I have a Glow Worm Swiftflow 75 which has been working fine for hot water all year (worked fine for CH last winter too) with the exception of the odd top-up. But now I've started to use the heating again this winter it's playing up. When I turn on the CH the pressure rockets up to max then gradually falls (I assume this is due to the PRV kicking in), then when I turn it off again pressure drops to zero.

From what I have read so far I'm guessing this is a problem with the expansion vessel or a blockage in its connecting pipe? If so how do I check/clean the pipe and check/top-up the pressure in the vessel? What should the pressure in the expansion vessel be? Am I even on the right track?

I'm also slightly worried that the pressure reaches well above 3 bar before starting to drop (obviously I haven't tried this too many times!!!). Could the PRV be faulty too or is this normal?

Apologies for the long-winded post and all the questions but I'm too broke to call someone out!

Thanks very much,
Rich

 

[ChrisR]

To recharge pressure vessel

Find where you connect air pump (car tyre type) on the PV
Drain water from a drain cock on the ch system a bit beyond pressure zero at the boiler.

Undo air valve cap and press central pin, note whether water comes out of the PV valve
Pump it up to say 12psi.

Refill water with filling loop , to 0.7 bar (others have other preferred levels).

Done.
Check that the PRV pipe is not dripping. If it is, it has to be dealt with.

 

[R6Rich]

Thanks ChrisR - lightning quick response!

 

[R6Rich]

If anyone else has got anything more to add that would be great - I need all the advice I can get

Thanks guys!

 

[ArtfulBodger]

ChrisR has covered it all and all thats left is an explanation of what he wrote:-

The EV has a rubber diaphram in it about 5mm thick. Half of the EV is supposed to hold compressed air, the other half is full of water. Over time air seeps through the rubber into the water side in much the same way as air will be lost from a cars tyres over a period of time.

He told you to drain the water from the system to a bit below zero on the pressure gauge. This is to ensure that the next step of charging the EV is not pushing against water and giving a false reading.

He then said to check the EV to see if any water comes out of the valve. If you're lucky you won't see any. If you do, you will have to replace the EV or, more likely, add an external EV somewhere on your system.

You should then use a decent pressure guage to check the EV, do not use the one fitted to your footpump 'cos it's crap. Hopefully you will see a figure significantly less than 7lbs per inch. You will now need to pump it up very slowly & carefully to about 1 bar. Do not do it too quickly or you may rupture the diaphram.

Next, repressurise the system to a low figure, this will give you the best chance of avoiding too high a pressure rise as the system heats up.

Lastly, the PRV has operated & so there is a good chance that it hasn't re-seasted itself properly because of all the crap in the system. If this is the case you will continue to lose pressure via your dripping safety discharge. If you do need to change it don't worry as it's not too difficult or expensive if you do it yourself.

Thats it really. I am now wondering why I wrote all this down as you had a perfectly good answer already

 

[ChrisR]

Thanks team! Perhaps this thread should become a reference for all the other people who ask..?

 

[R6Rich]

Can't thank you enough - cheers to you both.

I did understand ChrisR's post but still wasn't sure about the PRV allowing the pressure to hit max. That was a brilliant dummy's guide though ArtfulBodger which this dummy will definitely find extremely useful!

Thanks again chaps! - I really appreciate your time and effort.
Rich

 

[ChrisR]

One bit which may aid understanding:
when the water gets hot it expands to squash the air in the PV. So when all the air has gone and the pv is full of water, there's nowhere for the water to go. The pressure rockets up when the boiler heats. When it gets to 3 bar the Pressure Relief Valve open and lets water out. Then when the system cools the pressure goes down to zero.

Signs that there's very little air to squash in the pressure vessel:
You find that opening the filling loop makes the pressure rise very quickly,
The pressure rise when the boiler heats up is more than it used to be. Normally it wouldn't be more than about 0.5 bar more.