Ravenheat Condensing Combi Playing Up

[revjames]

My boiler is a Ravenheat CSi85A (T)

Installed about 9 years ago. Never had any issues with it until recently.

Noticed water outside coming from the over pressure vent pipe. looked like water had been coming out for a while. checked filling loop valve on cold water side and it did seem to be passing water continually (whatever position valve was in). So fitted an isolation valve between the CW and the one way valve on the heating loop.

The pressure on the gauge climbs from 0.5bar to 4 and results in the heating water being vented. I was told by someone that there could be leakage between the hot water circuit and the heating loop (failed matrix) I turned the cold water off and opened the hot tap - the gauge did go up slightly.

Just ran heating with cold water turned OFF at boiler and pressure climbed from 0.5 to 2.5 bar in 10 mins. I turned it off.

Any ideas chaps (and chapesses)

 

[kerching]

No!

but I had a customer who had an iffy boiler and the plumber turned up and re pressurised the 'bladder' or some such thing inside it. problem cured

just saying

 

[revjames]

expansion vessel. yes I did wonder. the thing is (cheapskate I know) I got a massive bank holiday discount about 9 years ago and ended up paying approx £400 for a condensing combi which for the most part hasnt skipped a beat - other than blowing main circuit board thanks to DNO (who paid for the repair - eventually)

So not looking at spending too many £££s on it

 

[ProDave]

+1 for expansion vessel

Start by checking the air pressure. If it's the sort of expansion vessel that hangs on a bracket and is connected with a flexi pipe, just pick it up and you will tell instantly if it's full of water as it will be way too heavy.

 

[revjames]

OK so should it be full of water - or air?

 

[ProDave]

Mostly air.

 

[Rob_the_rich]

expansion vessels can have both water and air in them. they are split down the middle by a diaphragm with a pre-charge of about 1 bar on the air side. The air filling valve is a shraeder type, such as on car tyres, and can be re-pressurised with a foot/hand pump. But you have to isolate the flow and return valves under the boiler and drain the boiler before you can test or adjust the pre-charge pressure.

it sounds like the pressure relief valve might need changing too, they should open at 3 bar, yours seems to open at 4 bar.

Edit; if the diaphragm has split (sounds probable), you will not be able to acheive the pre-charge pressure and therefore need a new expansion vessel

 

[revjames]

thanks for the replies so will check the expansion vessel.

 

[revjames]

Just had a look. vessel right at the back of the boiler. Not very accessible. Spoke to a heating engineer and described the bproblem and he immediately said heat exchanger. Looked into this and there seems to be 2. A big one that gest heated by gas flames and a smaller one at the back low down with 2 sets of pipes going through it. My guess is that this one has the HW and CH pipes going through and the CH heat the HW am I right and could this be where the pressure is going?

 

[SLIPSHOD & SLAPDASH]

Even though the pressure vessel is tucked away , its Scrahder valve will be easy to get to as its a common service item. I think its normally only a couple of bar pressure & its common that when pressures low the boiler pressure rises. However i am only a electrician and not a member of the better trade, plumbers   :slap

 

[Rob_the_rich]

I do not know why that heating engineer said it was one of the heat exchangers.

It does not sound at all like a problem with either heat exchanger. If the main heat exchanger is blocked it would overheat and lockout. If leaking, system would lose pressure.

If there was a leak in the matrix of your secondary heat exchanger so that mains water went into the system it would increase the pressure regardless of whether the boiler is running or not, but you tested it with the cold water inlet to the boiler turned off and still got a pressure rise.

it still looks to me like the expansion vessel.

Sometimes, it is impossible to change the expansion vessel without taking the boiler off the wall. In which case plumbers fit a new expansion vessel somewhere else, eg cupboard below boiler, the new expansion vessel is basketball sized and is usually cheaper than the one in the boiler.

 

[SLIPSHOD & SLAPDASH]

All combi's i have  seen have only 1 in pipe & 1 out pipe to the heat exchanger, nothing else. If its gone it will leak so try the expansion chamber first

Found this leak if you havent got a manual http://www.manualslib.com/manual/573703/Ravenheat-Csi85a-T.html

 

[revjames]

ran boiler for half hr, no pressure at all showing on gauge when started - rising to 3.5 bar - at that point I turned it off. still not sure what the expansion vessel actually does and how it can make pressure go up?

 

[NozSpark]

If the expansion vessel isn't working then there's nowhere to the hot water to expand to and the pressure will just go up and up

 

[Rob_the_rich]

with combi boilers, the water in the heating system is a closed system. That is why you have to fill it up from the mains using the filling loop. When filled, the loop (braided flexible pipe) should be disconnected so that there is no possibility of the system being filled continuously (as you had found, having to install another valve), and also no possibility of dirty water in the system contaminating the mains water (it can happen even if a one way valve is fitted).

Water expands when heated. In a closed system there is an expansion vessel fitted which can accommodate the expansion of the heated water. The heated water pushes against the diaphragm and is buffered by pressurised air on the air side of the expansion vessel.

Common problems are loss of the pre-charge pressure (check instructions for the actual figure), or a split in the diaphragm. It needs to be pressurised on the air side to give a greater volume than just system pressure alone, to allow for the greater volume the system water takes up when hot in a closed system.

The pressure relief valve is a safety valve which should stop the pressure in the closed system reaching dangerous levels.

Some CH systems have high water volume radiators, or have many radiators, and the volume in the boiler's expansion vessel is not enough to accommodate the expanded water. A secondary expansion vessel would then be needed to be installed somewhere. This would become apparent on fitting the boiler, or by adding "school-type" radiators to the system.

Phew. Hope this helps.

 

[revjames]

Thanks Rob, and Nick and Slips and anyone else I missed. That all makes perfect sense to me now. I shall chack the pressure on the shrader valve. I will also check what value it should be in the manual. I guess it will need to be pumped up somehow.

 

[revjames]

OK just located the schrader valve, not easy to get at at all! managed to push a pen in and a squirt of water came out. not much but none the less water so I take it that means the vessel is knackered?

 

[ProDave]

Yes, only air should come out. So the bladder inside is punctured.

Replace the expansion vessel and all your troubles will be ended.

 

[NozSpark]

If the boilers expansion vessel is difficult to replace then you can fit a standard one on an adjacent bit of pipework as said before

 

[revjames]

I just pumped it up to 0.5 bar (air pressure) with a bike pump. Gauge on boiler went from 0.5 to 2.0 bar. Fired it up and pressure went up quite quickly this time. Went to top bedroom and bled rad which was now full of air. so expansion tank it is. I could get the existing one out in situ if I remove the flue or I could fit one like this#

https://www.plumbnation.co.uk/site/altecnic-reflex-18l-heating-expansion-vessel/?gclid=CNy81bPj6cQCFTQatAodrFUA9g

Thanks for all the input. I didnt want to rush into a diagnosis and like to get all the facts and learn about the thing in the process before acting. At least its not a new boiler!