Gas Combi losing pressure

[MarkM]

Advance apologies for the long post but I thought it best to try and give you as much background as possible.

I have a Worcester 280 gas combi boiler which was already in the house I moved into approx 18 months ago. I'd been experiencing problems with the boiler cutting out when using HW and although I'd depress the reset button it would take ages to refire and would soon go cold again.

I got a plumber out (Corgi registered) but got held up at work so it was just the missus about when he came. Apparently he simply bled the radiators and used the Cold Water In knob to get the pressure indicator back up above 1 bar to about 3.

The pressure would still go down every now and again but in my naivety I would simply add more cold water (after reading other messages I get the feeling this was not a good idea!). Later the kitchen units which were below the boiler started to get rot showing on the bottoms and after ripping them out I discovered that there was a very small drip every now and again from where two pipes were connected. I sorted this out, monitored the pipes for 2 wks and put the units back thinking my problems were now solved. The pressure still went down from 3 bar to 1 bar perhaps over the course of a fortnight but I thought nothing of it.

Now today the pressure has dropped to zero and even when I open up the Cold Water In knob it drops straight back down in a matter of minutes. I've had a good look around for any signs of leaks but can find none. I'm trying to delay ripping out the kitchen units again and after Xmas and a new baby I really could do without having to get someone out but I think it might be inevitable. If anyone can give me any pointers on the sort of thing a plumber should be looking for at least I'll feel a little easier that I'm not about to be ripped off.

Thanks for your time.

 

[ollski]

Has the pressure actually gone from your system when it reads 0?, I mean it won't start up, no pressure to bleed rads etc. The gauge can fail.

 

[ChrisR]

IF you've had the pressure up to 3 bar then the Pressure Relief pipe (through the wall) will have been discharging. You shouldn't set the pressure above about 1.5 max. It WILL drop if the PR valve is leaking.

Search the forum on Expansion Vessel too.

 

[cmyers_uk]

I had the same problem with my Worcester 360 Combi. What it turned out to be was that when the pressure went above 3 bar the Presure Release Value opened and water escaped , one the pressure was below three bar the valve close but because of dirt / old age / unkown it did not seat properly and water dripped slowly out. You can check if this is happening by looking outside where the boiler is situated as there is usually a pipe. (The PRV on mine has a bright red knob that can be turned to manually open the valve). I replaced this for £6.50, your model £6.20 , in the manual it explained how to do it (two nuts if memory serves me right) for prices see here

Once this was replaced I didnbt lose any more pressure, but in my case the pressure still went over 3 bar. The normal working pressure for me is between 1 - 2bar at most , usually 1 - 1.5. This was caused by the pressure vessel failing. You can check this by removing the cover on the large red cylinder there is a car type value check the pressure , mine had water coming out which means the diaphram had gone I replaced this very easy to do explained again in the manual for £38 see url for prices.

Once this was done no problems since.

Hope this helps , at least you know from the url what the parts cost!

Chris

 

[MarkM]

Many thanks all for such a quick response.

Ollski - I am still getting HW/CH but the gauge does go up and now doesn't drop immediately to zero like it was yesterday.

ChrisR - thanks for the correct pressure advice.

Cmyers_uk - Thanks for all the details. I've checked outside and my pipe runs down to a drain. It does seem there has been water omitting from it. I can't locate a PRV anywhere. The pipe just goes straight into the back of the boiler. The other 5 pipes/outlets/inlets all have screw valves (at least that's what I presume they are) but the pipe that runs outside (with a sticker "safety valve") has nothing.

When I came in this evening the pressure was just above zero after I left it at about 1 this morning. I've ensured all the radiators are bled (a couple had a very small bit of air) and the pressure now seems to be hovering around the 1 bar (it drops to this after a couple of minutes when I put it up to 1.5). I guess I'll see tomorrow morning if it has gone all the way down again. I'm still getting HW and CH so touch wood it will function a little longer.

I don't know if this is related at all but quite often the boiler will take a few minutes to fire itself up. When I depress the reset button it stays depressed even after the boiler has fired up again and the can stay like this for weeks before eventually popping back up.

Thanks again for all your assistance
- Mark

 

[ChrisR]

The Pressure Relief Valve is inside the boiler - red cap usually. You may have to drop a front flap or similar to get to it.
Reset buttons are often "loose". If it ain't broke ...

 

[cmyers_uk]

Mark,

Go to here
Click the technical button at the bottom
Click CDi
Click System Layout.

You will then get a picture of the boiler showing where things are. Obviously pick the exact boiler that matches yours. But try the example above as you will see a good picture showing each of the components.

If your pressure is dropping you have leak somewhere. To test if its the PRV top up the water until its at say 1.2bar. Dont turn on the heating or hot water and give it an hour or so , has the pressure dropped. During this time look at the pipe outside has it been dripping water is so then it is probably for PRV leaking which is very easy to change yourself. If the pressure does not drop turn on the heating , watch now how high the pressure goes if it goes above 3bar then the value will release and vent water quite correctly and the problem is in another component , check the expansion vessel for correct pressue (car tyre guage).

It really is a matter of finding what bits leaking under what condition and fixing the cause.

Regards

Chris

 

[COG]

if you want to check the pressure vess the air valve is at the base so will tend to pass water as soon as you tap it if the diagphram has gone. If it has gone its one of the easiest to change ,held with one sliding clip one bolt and a screw to hold the clip.don't turn off the isolating valves they will leak for sure.

 

[MarkM]

Thanks guys. I reckon the PRV diagnosis is my first port of call. When the HW/CH is on the pressure stays around the 1 bar mark. Once they're both off however it drops to almost zero. My radiators also needed bleeding again so there's definitely some air getting into the system.

I'm going to need to remove the cylinder to get to the PRV at the back so will have to wait until I have a an hour spare with some peace and quiet

I'll give you an update over the next couple of days to let you know how I get on.

Cheers, Mark

 

[MarkM]

Well so much for the "update over the next couple of days" - my daughter's had chicken pox and boiler maintenance got put on hold!!

Anyway, I ordered a new PRV from the link that Chris kindly provided and managed to replace the old one. It's been in for almost a week now and the pressure hits 2 bar when CH/HW is on and then drops to about 1 bar when neither are in use. I haven't had to top up with cold water and it all appears to be working well - which in this cold weather is a relief not having to come downstairs in the morning to fire it up!

Thanks again for all your help and advice with this - saved me a lot of hassle and no doubt money. Keep up the good work.

Cheers

Mark

 

[COG]