Pressure problems - Vokera Syntesi 29e

[daveread2000]

I am new to this website (and to tinkering with a CH system) and have found the forum very informative. I have used what I have read to try and solve a problem we are having but would appreciate some feedback on what I have done to see if there are any other suggestions as to the root of the problem.

We have a Vokera Syntesi combination boiler and when the CH started coming on a week or so ago we noticed that the pressure was down at almost zero. I topped it up using the filling loop to 1 bar. I also checked all radiators and found no leaks.

When the heating came on, the pressure in the system rose to over 3 bar and the PRV started dripping. When the system cooled the pressure was back down to about 0.2 bar.

With the system cold, I located the expansion vessel and depressed the valve at the top. A small puff of air came out then stopped. No water came out. I used a pump to increase the air pressure to 1 bar. As I did this, the pressure in the CH system also rose to about 1bar. Was this supposed to happen?

Now when the heating comes on, the presssure still rises but now it goes from 1 bar to about 1.7 bar. Does this seem like a normal increase in pressure?

Overnight last night (and after the heating had been on this morning) the system pressure had dropped to about 0.3bar. It's raining at the moment so hard to tell but I think the PRV is dripping at a rate of about 1 drip every 3 mins. Could this have caused such a pressure drop? From what I have read, I understand that I probably need to replace the PRV. Is this correct?

My final question (I think) concerns the fact that we have done a lot of 'topping up' recently. From other posts I gather this means I should put some corrosion inhibitor into the system. How do I go about doing this?

Sorry to ask a lot of questions that may have been addressed elsewhere but as a complete newcomer to things like this I would really appreciate some confirmation that I have been doing the right things.

Thanks.

 

[Gasguru]

Bleed all radiators.

Release water and drop the system pressure to zero (may as well use the safety since you will need to replace it).

Check the vessel pressure...should be about 0.8 Bar for average height system.

Pump up if necessary ensuring the system pressure is zero ie. release system water if the gauge rises as the vessel is pumped up.

Easiest way to introduce inhibitor into system is via a radiator bleed point...Fernox and others have suitable inhibitors for injection.

Replace the safety and set COLD system pressure to 1 Bar MAX (for a typical property).

 

[MANDATE]

Your problem all stems from the expansion vessel.
When it was new it was charged with air to about .8bar. before it it came anywhere near water.
This meant the whole volume contained air. When the water gets heated and expands, it volume increases and enters the expansion vessel. This compresses the air and increases the pressure. the water pressure and air pressure are the same. So starting at about 1bar its designed to go up to about 2bar.
Now if the valve on the vessel has leaked over a long period it will have lost most of its charge pressure and volume in the vessel will be much reduced.
Now when that smaller amount of air gets compressed the pressure increases far more than it would normally, so instead of going from 1 to 2bar its more like 1 to 4bar. But the PRV opens at 3bar.
When you re-charge the vessel its easy to pump to 0.8bar, BUT!
There's always a but! there's another requirement. The vessel must basically have no water in it. So as you pump it up and flex the diaphram you need to expel the excess water.

Also the PRV once opened can be the source of another problem, cause they don't seal properly due to dirt etc

 

[JulieMia]

Hi all Julie here, mad DIYer but don't want to try my hand on this.

I had a good look around and couldn't find an answer to my question.
Water pressure drops in our syntesi 29e and we need to fill it up 2 to 3 times a day.

I found a schrader valve on the expansion vessel behind the boiler.
Only air coming out but sounds like very low pressure and then
I found another one on a cap which is at the top of a canister kind of thing behind the pump?
Water's coming out of this one.

Any advice suggestions and price guidance would be very much appreciated.

 

[Dan Robinson]

You have a vleak somewhere.

Search the FAQ on expansion vessels and it will show you how to recharge.

also check the pressure relief pipe outside isn't dripping.

If so then see above, then change safety relief pipe.

If they are OK, then you need to start hunting for leaks.