Vokera Synesti 35 High Pressure when on

[davidsl500]

Hi all. I have a problem with my 6 year old Vokera Synesti 35 Combi Boiler. I have provided as much information as to the story to date. Sorry if it’s a bit long !

Day 1. Came home to find the red warning light flashing with an error code of 4 – Low Water Pressure. Checked the gauge and it was sat on 0.2 bar. Checked with the missus to see whether she had been bleeding radiators (again lol) and no, she hadn’t touched them after the last time she did it 4 weeks earlier and caused the low pressure warning. So I refilled the system back to 1.2 bar (1 bar +0.2 bar for 2 metres from top of boiler to highest pipe run). Reset boiler and all okay.

Day 2. On the morning the pressure gauge was at 0.5 bar and had to go to work so didn’t touch it. By the evening it was down to 0.2 bar. Refilled the system back to 1.2 bar and went leak hunting round the rads and pipework in roof space – nothing found there. Switched on the system for the evening and the pressure gauge went up to around 1.8 bar when hot. When it switched off that night I rechecked the pressure gauge and it was down to 0.6…. I refilled the system back to 1.2 bar and noticed a leak from the bottom of the boiler. Took the casing off and traced the leak to the Automatic Air Vent behind the pump. I surmised that the valve was faulty and was venting air and water though I had not seen any evidence of water leaking from the boiler until the 3rd refill?

Day 3. Visit to Plumb Centre for a new AAV and fitted it. 10 mins, job done I thought…..nope! The first mistake I made was to use the PRV to partially drain the system down - well it said to use it in the Vokera Installation manual ! Up to this point I had not checked for a leaking PRV by the way-thinking that the AAV was the obvious culprit. Anyway, refilled the system to 1.2 bar and heating switched on pressure reached around 2 bar max and when switched off we were down to 0.2 bar…. Of course the PRV had been leaking since I used it which could have thrown the red herring into the system…

Day 4. New PRV fitted (thanks Plumb Centre) and system refilled to 1.2 Bar. Switched on heating and kept and eye on the gauge and watched it climb all the way round to 3 bar before I switched the system off. This took around 10 mins from a cold system. The system is now off and the pressure has gone gradually back down to 1.2 or a little below but the PRV may have operated briefly. It’s not leaking now so the new valve is okay. Over the last few hours since it has been off the gauge has been stable or slightly down as the water cools.
I am slightly stuck in checking the pressure of the Pressure Vessel at the moment – I have just about reached the valve and pressed the pin briefly – air heard escaping but no water seen. Because the boiler was mounted on a bare wall that has now been insulated and plaster boarded I have a little work to do to get sufficient clearance to get my pump and gauge in. This I hope to achieve tomorrow evening. List of swear words ready....

So my question is – am I right in suspecting the Pressure Vessel is down on pressure and causing the rapid rise in pressure when the heating is turned on or do you think the problem is elsewhere? Any other fault finding tips please? I shall let you know what happens next !

 

[Agile]

Unless you measure the air pressure in the EXV then how can anyone know?

Tony

 

[davidsl500]

Thanks for the reply, I can appreciate what your are saying Tony, I shall be excavating tonight after work and getting a pump with a longer hose to get to the valve. It was a bit late after midnight to go out and get one !

I suppose I was asking from a generalised point whether the characteristics of a EXV when it is low on pressure, but not letting in water, is to cause the rise from 1.2 bar to 3 bar in the space of 10 mins when the boiler is switched on? I have tried to document the events as they happened in case they give clues to the likely fault.

From my first post, I am presuming that if I hadn't used the PRV to drain the system down to replace the AAV the pressure would have reached 3 bar at that stage - as it was, the PRV did not re-seat fully and was thus bleeding off water and it never got past 2 bar. This also explains the almost zero reading on the gauge when the boiler was turned off.

As a footnote, the gauge this morning is reading 0.8 bar this morning as I left for work, from 1.1 at about 2.00 last night and the PRV outlet is dry.

I shall report back this evening when I have done the pressure check on the EXV

 

[davidsl500]

So the latest update. I have’t got home yet but got the missus to follow instructions – which I think is a first!

Opened a rad bleed valve to get the boiler pressure gauge down to zero and then closed it off. Foot Pump attached to EXV – air heard coming out of it as the pump valve was locked on it but the pressure gauge read zero. Pumped up EXV to 15 PSI and told her to leave it on for a bit to see if it went down – nope, after 10 mins it was still reading 15 PSI so the foot pump was disconnected. Boiler gauge still on zero so this was refilledto 1.2 Bar and bled the radiators – water came out of them all straight away. Topped up boiler gauge to 1.2 Bar again (only slightly down after the bleed) and switched on the boiler at the isolation switch – didn’t turn the CH programmer on at this stage. The pump circulated the water and gauge went straight down to zero. My thoughts were that there was air in the pipes in the roof space still. Topped up boiler back to 1.2 Bar and switched on the boiler again. This time the gauge went down to 1 bar so the programmer was fired up to see what happens. Pressure gauge climbed steadily past 2.5bar and at this stage a hot tap was opened to see what happens and the boiler gauge did stop rising whilst it was open. The CH was turned off and the boiler isolated after its cycle - I didnt really want it hitting 3 bar and messing my new PRV up!

Any thoughts chaps? The problem with this boiler is that the gauge is behind a drop down flap so its not something you notice when passing through to see what it is normally doing. I am wondering whether the AAV leaking water in the first place was just a casualty or pure coincidence of a larger issue that was developing anyway?

 

[CBF]

i would still suspect the EV, did you leave the bleed nipple open when you re-pressurised the EV if not then you won't have 15 psi in the EV, you need to have an open end either the bleed nipple, prv or a drain cock or you will get a false reading, water will come out of what ever you have open when you pump it up

 

[davidsl500]

i would still suspect the EV, did you leave the bleed nipple open when you re-pressurised the EV if not then you won't have 15 psi in the EV, you need to have an open end either the bleed nipple, prv or a drain cock or you will get a false reading, water will come out of what ever you have open when you pump it up

I was wondering about that. I followed the "how to guide" on this side and it said to close the bleed nipple once the gauge reached zero and not leave it open while re pressurising the EXV. I have been reading the forum and it seems that the general concensus is to leave a bleed open - I can understand the logic to that. I shall go home in a bit and try it leaving the bleed open this time and depresurise and represurise the EV again and report back. Thanks for your reply

 

[davidsl500]

i would still suspect the EV, did you leave the bleed nipple open when you re-pressurised the EV if not then you won't have 15 psi in the EV, you need to have an open end either the bleed nipple, prv or a drain cock or you will get a false reading, water will come out of what ever you have open when you pump it up

I was wondering about that. I followed the "how to guide" on this site and it said to close the bleed nipple once the gauge reached zero and not leave it open while re pressurising the EXV. I have been reading the forum and it seems that the general concensus is to leave a bleed open - I can understand the logic to that. I shall go home in a bit and try it leaving the bleed open this time and depresurise and represurise the EV again and report back. Thanks for your reply

apologies for the double reply I hit quote instead of edit !

 

[davidsl500]

So, the update. Drained the system down a bit and left a bleed valve open. Before depressurising the EV I checked the pressure reading at it was 15 PSI so was not feeling hopeful... Depressurised it and air only coming out of it. Repressurised it to 15 PSI filled the system to 1.2 bar, bled the radiators and switched on the central heating . After and hour it was 1.7 bar so that seems to have done the trick.

Only problem I have now is some cold rads down the one side of the Bungalow. The bled water okay but nada on the heat front. I presume that there are some air locks in the roof space in the pipes that feed those rads. The only problem is that whoever installed the system didn't bother to put any bleed valves up there, duh ! So I shall be reading up on "cold rads and bleeding" next! Still the boiler seems to be stable so thats half good news!

 

[davidsl500]

So the saga continues.......so yesterday evening the boiler pressure gauge had stabilised at 1.7 bar after an hour of being switched on but only 4 of the 11 rads were actually hot, the rest being stone cold. All rads were full of water. So I turned off the working rads and that kicked in another 2 rads which were then turned off etc., until all the rads were functioning. Turned all the rads back off and turned the ch off whilst I gave them all a quick bleed. Bit of air in a couple but not a lot. Turned on the ch again and kept an eye on the boiler gauge which crept up to 2.5 bar and stayed their whilst the ch was on for a few hours. After it had switched off the gauge went down to 1 bar and has remained there. This evening its back to 2.5 and static.

I am not overly happy with and increase from 1 bar cold to 2.5 bar when operating but its working and I am warm again!

Anyone any ideas why there should be such a large increase? Is the EV still under question?

 

[davidsl500]

I did a little experiment last night / this morning. From my last post, When I originally switched on the system after repressuring the EV and refilling the system only 4 of the 11 rads worked and the boiler gauge read a steady 1.6-1.7. As I got the other rads working by turning off the already working ones, the boiler pressure gauge went up to 2.5 and remained stable with the heating on (with all the rads open)

I closed the rads that did not work immediately just to get back to the 4 that were to see if the pressure returned to 1.7 bar with the heating on but it did not. Leaving the rads closed overnight (pressure returned to around 1bar when cold) this morning the boiler gauge was 1.7 with the heating on as I opened up the rest of the rads the boiler pressure returned to 2.5....

One other comment I should make is that originally the system was 9 rads and this has been increased to 11 rads over the last 2 years as we added on a utility and ensuite. I wonder if the expansion vessel is too small with the increase in rads and its always been running that high? Unfortunately I have never really looked the gauge as its hidden behind a flap. I have a vague recollection that it always ran about 2 with the original 9 rads. It is a decent sized 3 bed bungalow with all the pipe runs in the roof space so I wonder whether I have hit the limit for the expansion vessel by adding the extra rads?

 

[MANDATE]

Read your problem with interest!
There's more to the expansion vessel beside getting the initial pressure correct! It is essential all the water is forced out to give a maximum amount of 'air' for compression. If the 'air' volume is halved the pressure will double.
The schrader valve may leak a little air over time, the air pressure drops and the water pressure being higher moves the diaphragm. So you finish up with less air volume and more water volume in the vessel.
Adding extra radiators increases the total volume of cold water in the system so when this water is heated there will be more expanded water for the vessel to deal with.
With some of the radiators turned off the water in them will not get hot so the amount of expansion will not be as great and explains why pressure goes to 1.7 bar as against 2.5 bar.
I would think an increase from 1 bar to 2.5 bar is acceptable but if the vessel loses air pressure over time the 2.5 bar will creep up.
When the additional radiators were added the size of the vessel should have been taken into account and perhaps an additional vessel added.
You mentioned the Hot Water and the reason the pressure does not increase much is because it only uses a small proportion of the system water to feed a heat exchanger. With a combi you can't have water going through the heating system while running Hot Water.
Also if any radiators have 'air' in them, then that 'air' is compressible and acts in the same way as a expansion vessel, so when it gets removed and replaced with water you would expect the water pressure to increase slightly with the same conditions

 

[davidsl500]

Thanks for the reply Mandate. The en suite and utility were added a year apart and the plumber different in each case so both were just adding one rad and each may have thought that there would be spare capacity to deal with that. I presumed that once with all the rads on we reached 2.5 then closing off some rads would have no effect with the system still running as it was already pressurised. This is why I left them closed and the system cool overnight back to 1 bar to see what the result would be. I don't like the 2.5bar reading - as you say, it wouldn't take much for a slight loss in the EV to give me problems later. Also, I would rather see the system at 1.5 bar rather than 2.5 bar as there is less stress on all the plumbing joints. I hadn't thought that as more radiators came on line it meant my "temp extra EV" re air in the pipes was assisting so thats a good point.

I think I am going to get an external EV and add it into the system anyway - it may be a bit of over-engineering but it would do no harm and it will save me skinning my knuckles reaching the internal one! Thanks again for your thoughts. I shall report back when I have fitted it. For now I think I will close off a couple of rads in rooms that we dont use to reduce the pressure safety margin a little

 

[MANDATE]

If you set the cold water pressure to 1 bar it won't stay at 1 bar. As expansion takes place the pressure is bound to increase. The pressure it increases to will depend on the size of the vessel and it's set air pressure being maintained.
An increase of approx 1 bar is about the norm.
[/quote]

 

[davidsl500]

Thanks for the comments. I appreciate that the cold pressure won't stay at 1 bar - it has been pretty consistent so far but the ambient temperatures have been pretty constant here. I have locked off the rads in two bedrooms and one of the hall rads and the max gauge pressure has settled at 2.1-2.2 with the boiler water temp at 70 degrees. I am happier with that but its only a short term "workaround". Incidentally, the rads that I added - one was a 1400x600 Double and the other an 1800x450 chrome vertical so I think I have added a bit of volume there.

As its very difficult to get to the pipes around the boiler and as the boiler EV is working okay can I add a secondary external EV remotely into the system rather than close to the boiler. We have an airing drying cupboard with a traditional radiator in which would hide the EV nicely and would be easy to Tee off?