no combi pressure

[worthy]

I have a Vaillant turbomax combi boiler, which has lost all its pressure, the temp reads around 40 and the central heating works fine, but the hot water has gradually stopped. The hot tap had to be on full for ages to get it to trigger the boiler, now I get nothing.
How do I get the pressure back up?, do I have to refill the system, if so how?

 

[cleddy]

I'm not an expert on heating, and I don't know the particular boiler you have, but I have had 2 combi boilers.

With these, if the boiler needed refilling, then the heating stopped working, and the hot water flowed, it was just cold.

It could be a blockage, although if it is, I don't envy you having to search for it.

My boiler has a troubleshooting guide with it, I could have a look and see if this problem is mentioned, but I'm at work at the mo.

 

[robmorphet]

DOES the combi have a vent (similar to a bike/car tyre valve)? Press this in and it may release the trapped air, and get you moving again. It worked on mine after hours of farting around bleeding pipes etc. (it was located on the big red pressure vessel agaist the wall, at the top. You may also find that the pump has on too, depending on which one it is.

I'm no CH engineer though, but it worked on mine and it is only a vent after all.

 

[breezer]

i am not a heating engineer, but do not release air from the big red cyliner ( i did once) the big red cyinder is the expansion vessel, when the water gets hot it needs some where to expand hence the expansion vessel.

Inside is like a balloon and all you will be doing is releasing air from the ballon. this in turn drops the system pressure which then causes either low pressure light (if fitted) to come on and just low pressure. it then needs to be re pressureised (the balloon) enter one plumber, exit large cheque (but i now have British gas, and the engineer did confirm about the pressure vessel that is how i know.

 

[Gees]

I am not a heating engineer.

I assume that because you have a pressure vessel the system is sealed....
The pressure vessel must NOT be bled. The whole idea being that the water has somewhere to expand to as it expands as it gets hotter.No air in vessel = hiss, as water escapes from weakest point. There is a pressure release valve that will be vented to the outside world so there will be no scalding water all over the place.
As for lack of hot water. Is the water from the tap cold or is there no flow?
If the CH is working the diverter valve may be sticky, thus not triggering the electrics to start the heating of the water.
I spent 15 years keeping my old combi going but gave up last year and got a £500 new one. Its a lot better and cheaper to run too.

 

[Aiyub]

The vent on the big red expansion vessel is used to "repressurise" the vessel ONLY. Do not bleed anything from that.

Valiant has another bleed port, often to the top right hand corner. Looks like a small grenade, ( best way I can describe it) You can bleed that port by slightly pressing the schraeder valve.

If in any doubt do not play around with your boiler. Im not sure if you need to be Corgi registered to try and attempt something like this.

 

[Gees]

Corgi only needed for gas bits

 

[worthy]

Thanks for all the help, but not sorted yet.
The hot water does flow, but is cold. Except when the boiler is on for the heating. Its as if it doesn't sense the tap is open, to trip the gas on.
the pressure still reads zero, whether this is related to the hot water I don't know. Can't find the car type valve to repressurise either

 

[Gees]

The pressure vessel is usually charged to about 0.8 Bar ( 11 psi)
The ch pressure is achieved via the filling loop from the cold water supply.
Pressure when cold should be 1 bar rising to 2 bar at full heat ( Approx).
The DHW taps when turned on produce a pressure drop with respect to the cold water input pressure. This is what depresses a diaphragm in the diverter valve and hence turns ON the burner. The cental heating pressure must be at the correct level otherwise the DHW will not work.
What does the pressure meter on the boiler say? Usually if the pressure is too low the boiler will not run and will not produce CH or DHW.

 

[drgl]

i have the EXACT same problem! The pressur gauge on the front is reading slightly below 1 Bar(only rises to 1.5 when hot),is it safe to pump air into this expansion vessal & does this sound like the cause of no hot water??

 

[COG]

ALL PRESSURE VESS ARE TO COPE WITH THE EXPANSION OF THE HEATED SYSTEM WATER ,THE PRESS URE IN THE VESS WILL VARY DEPENDING ON THE BOILER BUT MAINLY ON WHAT SIZE OF VESS AND THE SIZE OF TH SYSTE ,BUT MOST ARE BETWEEN 0.5 AND 0.8 BAR COLD WITH NO PRESSURE IN THE SYSTEM (NORMAL TYRE GUAGE WILL DO TO TEST). WAS YOUR ORIGINAL PROB THAT YOU HAD NO PRESSURE ON THE BOILER PRESSURE GUAGE IF SO THEN YOU NEED TO FIND THE TO UP LOOP FITTED BY YOUR PLUMBER ,USUALLY A SILVER HOSE WITH ONE OR TWO TAPS

 

[drgl]

OK,update:-checked pressure in the red vessel at the back-was low so have inflated to 0.9 BAR(as per manual) have refilled boiler so gauge reads 1.5Bar(cold) still only have hot water if tap is on full(or if the CH is on can draw hot water at any flow rate)heeeelp!..........

 

[Gees]

Check divertor valve for correct operation. ( It may be stiff )
What is the cold water input presure?
Make sure your stopcock isn't turned down.
If there isn't enough pressure drop the valve may not open far enough to trip the electrics but far enough to let SOME water through the heat exchanger. If the heating is on at the time the water will be heated as if the valve was closed. This will produce hot water at low flow rates with the heating on. When the tap is fully open maybe then the valve fully opens and the hot wter system works as it should.

I may of course be talking a load of twaddle

Good luck.

 

[drgl]

water pressure seems fine,i guess it's the diverter valve?? any ideas where to get one/how much to pay?? Thanks

 

[Gees]

DRGL you don't say what boiler it is you have. Try Plumb Centre ( or any of the many plumbers suppliers around ) Be ready for a possible shock when told the price.... last one I got was a few years ago and it was £79.00 ( +vat ) Ouch.........