Vaillant EcoTech 624 pressure mystery

[Seb1961]

Hi,

I have a Vaillant EcoTech 624 system boiler, around 7 years old.

Last week after having the boiler serviced (which inluded re-pressurising the expansion vessel), and when we first starting using the CH again after the summer and first cold weather, the CH worked OK for a day or two. But the next day the pressure plummeted to 0.2 with an F22 fault code.

I have since bled the radiators (there was some air in the rads high up in the house) and added water to the system up to around 1 bar. If I then switch on the CH it runs OK, but after it shuts down the pressure falls again all the way down to 0.0!

I checked the PRV, and the waste pipe is completely dry, so no water has been discharged.

Today I bled the radiators again just to make sure, with the system being stone cold, and then filled up to 1.4 bar and started the CH. The pressure went up to 2.1, as expected, but then steadily started to fall while the CH was running down to 0.7, at which point I thought it better to switch it off.

I know that all this suggests a leak, but there are no signs of a leak anywhere.

What is odd is that if I add water, and don’t switch on the CH for a few hours, the pressure holds steady and does not drop. How come? (This BTW surely also indicates that there is no leak.)

What I don't understand is where all the water goes that has been added when topping up.

Is it possible that after not using the CH for many months the system has somehow lost water?

Any help anyone can offer will be appreciated!

Seb

 

[flameport]

I checked the PRV, and the waste pipe is completely dry, so no water has been discharged.

That isn't conclusive - the water coming out of there will be very hot, so would eveporate away quickly.

Put a plastic bag over the end and run the heating, if water escapes it will be in the bag.

If it's not there, then you have a rather substantial leak somewhere.
However it's likely the expansion vessel has either failed internally, or has been overfilled so is not working correctly. The water escapes through the PRV as it heats and expands, as there is nowhere else for it to go.

 

[Seb1961]

Thanks, flameport.

Seb: I checked the PRV, and the waste pipe is completely dry, so no water has been discharged.

flameport: That isn't conclusive - the water coming out of there will be very hot, so would eveporate away quickly. Put a plastic bag over the end and run the heating, if water escapes it will be in the bag.

Seb: I'll try that, but I should explain that my PRV wastepipe is inside the house in the airing cabinet, not outside. The copper pipe goes into a white swan neck waste pipe which is open at the top. I unscrewed the swan neck and it was full of dust. It's quite clear that no water has been through it.

In any case, the boiler's pressure never went beyong 2.2 bar, so the PRV could not have opened.

flameport: If it's not there, then you have a rather substantial leak somewhere.

Seb: That may be the case, but how come the boiler stays under pressure when I fill it, but don't fire it up? Before going to bed last night I put the pressure up to 1.3, and it held throughout the night. If there was a leak the pressure would have dropped, right? It's only when I run the boiler that the pressure drops either while running, or after I switch off the boiler.

flameport: However it's likely the expansion vessel has either failed internally, or has been overfilled so is not working correctly. The water escapes through the PRV as it heats and expands, as there is nowhere else for it to go.

Seb: Isn't a failed EV unlikely because the pressure would have gone up, rather than down? And like I said above, no water was discharged via the PRV waste pipe.

What about the question I asked earlier, is it possible that after a long period of not using the CH, the system (which has 11 rads) has become unbalanced with scattered pockets of air which cause these strange fuctuations in pressure?

Thanks,

Seb

 

[twgas]

I'd agree with flameport, the expansion vessel needs checking, even if in your infinite wisdom it is "ok"

 

[Seb1961]

I'd agree with flameport, the expansion vessel needs checking, even if in your infinite wisdom it is "ok"

I really don't wish to pretend to have infinite wisdom.

I checked it just now. No water is leaking from the valve, and the pressure is 0.9 bar which I believe is as it should be.

Also checked the swan neck again into which the PRV copper waste pipe goes. It had a lot of bone dry black gritty soot in it. It seems unlikely that water passed through.

Also checked everywhere again for leaks and found no evidence. I must have topped up at least 10 times, so I have no idea where the water is going.

If I top up the boiler and leave it off, the pressure holds steady,even overnight. How can that be if there is a leak?

At wits' end......

Seb

 

[twgas]

Is that (0.9bar) the air charge in the vessel? And how exactly did you check it?

 

[Seb1961]

Is that (0.9bar) the air charge in the vessel? And how exactly did you check it?

Mike, yes it's the charge in the expansion vessel. I used a a digital tyre prssure gauge. Are these not reliable?

 

[Seb1961]

Is that (0.9bar) the air charge in the vessel? And how exactly did you check it?

Mike, yes it's the charge in the expansion vessel. I used a a digital tyre prssure gauge. Are these not reliable?

Sorry, Mick, got your name wrong.

 

[twgas]

No probs, I've been called worse than that
Did yoy empty the boiler of water AND leave the drain point open?

 

[Bunnyman]

As above, did u drain boiler then check vessel pressure?
Yes u have a bad leak, it may hold static pressure when the heating is not running.
Is you cylinder mains fed or from a tank in the roof? If it's tank fed and the coil has gone in the cylinder it could be leaking into the water system from the coil.
Or it could possibly be the main ht exch leaking down the condense pipe.
Usually it's a leak on the system tho, do u have pipes under concrete? These are favourite

 

[Seb1961]

As above, did u drain boiler then check vessel pressure?
Yes u have a bad leak, it may hold static pressure when the heating is not running.
Is you cylinder mains fed or from a tank in the roof? If it's tank fed and the coil has gone in the cylinder it could be leaking into the water system from the coil.
Or it could possibly be the main ht exch leaking down the condense pipe.
Usually it's a leak on the system tho, do u have pipes under concrete? These are favourite

Thanks Bunnyman.

Boiler pressure gauge was showing pressure of 0.0 before I checked the pressure on the EV.

I'm not sure whether the cylinder is mains fed or from a tank. We do have one in the loft.

I had never heard of the main heat exchanger leaking down the condense pipe. We have been hearing water running away, but assumed that was the normal flow of the condense. If the heat exchanger is leaking down the condense pipe, will that involve a costly repair, and is there a way of checking that that is indeed happening?

Seb

 

[AL66]

Sorry - wrong thread!

 

[Seb1961]

As above, did u drain boiler then check vessel pressure?
Yes u have a bad leak, it may hold static pressure when the heating is not running.
Is you cylinder mains fed or from a tank in the roof? If it's tank fed and the coil has gone in the cylinder it could be leaking into the water system from the coil.
Or it could possibly be the main ht exch leaking down the condense pipe.
Usually it's a leak on the system tho, do u have pipes under concrete? These are favourite

I isolated the hot water cylinder and now the CH runs normally without pressure drops. What does that indicate? Would it be the coil that's got a leak? If so, would there be a lot of water leaking into the water tank in the loft? I thought that with a system boiler the whole setup is closed.

 

[Bunnyman]

👍

 

[Seb1961]

👍

I thought my troubles were over, but now I get this:

When I run the DHW only, the boiler runs for about half an hour and then shuts down. This may seem to indicate that the water in the cylinder has reached its temperature, but the zone valve does NOT shut. The pump runs for another minute or two and then stops. Almost immediately the boiler then starts up again, runs for two minutes, then shuts down and the whole thing repeats itself 4 or 5 times. At that point the cylinder thermostat shuts the zone valve down, so it seems that only at that point in time has the water reached its preset temperature of 60 degrees. What is telling the boiler (but not the zone valve) to shut down for up to four or five times before the water in the cylinder is at the right temperature? I have made sure that the temperature setting on the boiler is set higher than the temperature of the cylinder stat.

Thanks,

Seb[/b]