vaillant combi boiler

[Tim Smith]

Hi there,

I have a Vaillant Combi boiler (according to hte manual, it is eithera VCW GB 221H , 240H or 280H - Im afraid I cant find any indication on the boiler itself).

Over the past couple of weeks, I have noticed that although the boiler is on for central heating, the thermostat in hall seems to indicate the acutal temperature is lower than the set temperature by several degrees. I do this by listening for the click on the thermostat so I know it isnt incredibly accurate. In addition, the radiators are reasonably warm.

However, today on furhter investigation, I did notice that the pressure gauge on the boiler is indicating just below the first mark on the gauge which I think is 0.5bar. The instrucitons indicate that the pressure should be around 1bar.

According to the manual (and fairly obvious to even my limited knowledge) the water pressure needs topping up. The instruictions I have recommedn getting a plumber to do this but I dont fancy paying someone good money to do something that is probably straight forward (I have done this on a boiler at a previous house). The isntructions dont mention which is the correct valve for water inlet.

Can anyone tell me which is the correct valve to open and whether this could cause the symptoms I am seeing ?

Thanks

Tim

[andrewpreece]

I had a Vaillant 242: in that case the filling loop was a length of braided flexible pipe, with one end going to the cold water inlet pipe. There were two knurled plastic knobs on valves at each end of the pipe, and you had to open both in order to get water flowing in ( I think it is two valves to prevent back-contamination of the domestic water supply by pressurised water flowing back from the boiler ). I believe you have to open them in a particular order, though offhand I can't remember what order it is!

Your cold water inlet pipe, should be fairly easily identifiable as it will be 15mm and will be cold to the touch, if the HW and CH are or have been in recent use ( the gas pipe is 15mm but not so cold ). Anyway, that's my best to offer on the subject, perhaps someone with knowledge of the exact model can be more helpful. Oh, by the way, if your system pressure keeps falling, get it looked at, as continually topping the system up leads to corrosion and early failure.

Andy.

[Tim Smith]

Thanks Andy,

I think I have identified the cold water inlet - as you say it is cold ! It also has a T-joint. One side goes into the boiler (presumably for the hotwater) and the other (via a braided pipe and two valves) connects to a hot pipe. I guess this is teh connection into the sealed heating "circuit".

Anyone any idea which order the valves should be opened in ? I guess they could be defined as the valve at the hotwater "circuit" end and the valve at the end cold supply end.

Thanks again.

Tim

[rogersmp]

Funny old thing, I have exactly the same problem. My instruction reckon there should be a filling line somewhere on the central heatin return line. But I have looked high and low and cannot find on. I wa wondering if there is an auto fill mechanism, but cannot find it. To b honest the boiler was running ok, but I got a bit nervous running i when the pressure reads dead zero. Maybe this setup is geared aroun getting plumbers more work?

-- rogersmp

[andrewpreece]

I'm not too sure that it is necessary to open them in a particular order, thinking about it: the fact is, if you crack them both open your system will pressurise. I may be getting confused. These filling loops have a valve at each end so that you can disconnect them when you're finished - not that a lot of people bother! The theory is that either yucky combi water will feedback into the mains water if there is a leak in the filling valves/you don't turn them off properly, or that if the mains pressure exceeds that in your combi ( which it should do anyway ) that the system will sowly pressurise from the mains. Once it reaches 3 atmospheres the pressure relief valve will blow off and dump a lot of your CH system water out of the blow-off pipe ( the blow off pipe probably exits via your wall somewhere - it would pay to keep an eye on this pipe especially when the CH turns on of an evening to see if it is blowing off ).

Anyway, given that you are supposed to remove the filling pipe once finished with it, you can see that it needs a valve either end or you would have a gusher, either from the mains cold water end, or the CH loop end. So, ignore the fact that I talked about an order to things, and just crack both the valves open slowly. You'll want about 1 to 1.5 bar pressure in the system. You may have a leak in the pipework, or a punctured diaphragm in your pressure relief vessel ( big red doughnut shaped thingy, at the back of the combi somewhere ), if you coninue to lose pressure,

Andy.

[Tim Smith]

Roger,

When you say you have the same problem, do you mean pressure at zero or lack of temperature (tested in my rahter unscientific manner) or even both ?

Tim

[andrewpreece]

Has your filling loop been removed? They are really supposed to be removed once you've topped up the system. There will still be a connection point on the coldwater pipe and the CH return ( or flow? ). Some combis have built in filling loops: my Vaillant has two valves built into the underside of the casing, it takes two special little keys to open or shut the valves. It's all very inconspicuous.

Andy.

[Tim Smith]

Thanks all,

I took the plunge at opened the valves and the pressure increased on the gauge. Ill keep an eye on it and see if the heating is any better and if the pressure drops again.

Thanks

Tim

[Ed Sirett]

p

You must have a Eco/Turbomax/Thermocompact Plus model. About 5 years old or less. The OP has something from about 10-20 years ago.

[andrewpreece]

Yes, that's right, it's a Turbomax. Ed, we talked a while back when I was concerned that the HW from my Turbomax was hotter than I had it set when I installed it, yet I hadn't touched the HW temperature control: I was miffed because the Turbomax gives the impression from the display that the HW can be set to an exact temperature. I spent an entire day faultfinding and decided something must be broken, but I've come to the conclusion it's OK after all. I reckon the Turbomax only controls the CH loop temperature, and the HW temperature is determined by both the CH loop temperature and the temperature of the water as it enters from the ground. When I was concerned about the HW being hotter than I'd set it, a few months back, the ground-water temperature was 16C, about as warm as it gets! I shall have to twiddle the dial a few times a year to keep the HW temperature constant at the taps, but that's no big deal, now that I know,

Andy.