Vaillant ecotec 624 pressure (again)

[Seb1961]

Thanks to everyone who replied to my previous post earlier this week.

I have been having problems with the pressure on my Vailant ecotec 624. It was going right up to 2.7 and then, when switched off it came right down to 0.4 and needed topping up.

Since then the EV has been repressurised a second time by a competent heating engineer, but the problem persisted. Today he came back again and exchanged the little tap that allows you to top up the system as he thought water might be seeping through and he also replaced the PRV. He said there's nothing wrong with the EV since it's not getting hot which means it's not got water in it.

After he left I switched on the system and the pressure went right up to 2.7, but then, bizarrely, fell back to 1.2, which is the level he pressurised the EV at. It's been running now at 1.1/1.2 for around 50 minutes so quite normal.

Then after one hour it suddenly dropped to 0.6.

Has anyone come across this kind of behaviour in a boiler? Going up to 2.7 is too high, isn't it? Or are these fluctuations normal? Should the engineer come back again and perhaps replace the EV anyway? I'm losing faith in Vaillant. I thought they were the best?

Seb

 

[MANDATE]

Yes! the pressure will rise and fall when the heating is on and off.
Generally! you need the expansion vessel to have no water in it and set the pressure to around 0.8/1bar (you could check boiler instructions)
To ensure there is no water in vessel the 'water' side should be open to atmosphere and water pressure at zero when setting the expansion vessel pressure.
This is followed by setting the water pressure to the same pressure, this means the diaphragm is still biased to the water side leaving max 'air' for compression.
With heating running, volume of water increases and pushes against diaphragm, compresses air and pressure of both air and water increases.
Amount of increase should be around 1bar.
So ideally boiler pressure will increase from 1bar to 2bar.
Or even 1.5bar to 2.5bar.
2.7bar is still ok, but a little lower would be better.
You could lower the water pressure from 1.2bar down to 1bar or even 0.9bar and the 2.7bar should also come down by the same amount.
(Bleeding a radiator for few seconds will lower the pressure)
Or you could leave it as it is and see if the 2.7 increases.
My daughter has a combi which has had similar type problems due to loss of the vessels air charge and the PRV operating. I have it operating from 0.8bar to 2.1bar.

 

[The831Bunny]

How many radiators have you got on the system? A vessel pumped up too hard i.e. 1.5 bar for instance has very little capacity when coupled to a 10+ rad system. You may need an additional expansion vessel if it is pressurised correctly (Max 1 bar) and the pressure is still rising on heat up.

On a correctly sized and inflated expansion vessel, the system pressure should not increase more than 0.3 bar

 

[Seb1961]

Hi,

Thanks for the replies.

I'm aware that there is expansion when the CH/HW is running, but perhaps I wasn't very clear in describing what was happening.

When I switched the system on, the pressure went up to 2.7, then came down (system still running) to 1.1/1.2 where it stayed for an hour or so. Then (still running) it came to to around 0.6. So my question is: are these fluctuations normal while the system is running? What would explain the fluctuations in pressure?

Did the PRV open when the system went up to 2.7? It shouldn't open until the pressure gets to 3.0 bar, right? Once it opens does the PRV stay open which might explain the pressure drop right down to 0.6? It was installed yesterday and I wouln't expect it to have failed already. The water in the system is very clear and free of sludge so unlikely to have stopped the PRV closing again. So how do PRVs normally operate? Do they normally close again when the pressure on the system goes down below 3 bar?

This morning the pressure had dropped to 0.4 and I had to top up the system.

To answer The 831Bunny, we have 11 rads, which includes one smallish towel rail. Thing is, though, the system has been running for four years without any problems at all.

Just to reiterate: there are no obvious sign of any leaks anywhere.

In your view is there any point in replacing the EV? Do any of the symptoms I described point to a failed EV? I don't want to spend over £100 only to find that the problem is not the EV.

There's no water coming out of the EV valve.

I'd really appreciate some further thoughts on this as I don't think the engineer knows what to try next, short of replacing the whole boiler!

Thanks,

Seb

 

[Seb1961]

After writing my latest post I decided to double check if there is any air in the radiators and found that in two or three there was some. Previously I had been hearing some gurgling sounds in the rads when the system was running.

Could air in the system explain the fluctuations in pressure?

Seb