Boiler Pressure Keeps increasing - Vaillant Ecotec Plus 838

[Zishan]

Hello everyone,
I have a Vaillant Ecotec Plus 838. The issue i have is after the heating is switched on and then left it to cool over night i see the pressure has gone up.
For example yesterday it was set at 1.3 heating was switched on and when it reached its temp it went upto 1.9 so no issues. But when its left to cool over night the pressure shows 1.8 in the morning. The pressure in the expansion vessel was at 1.0 bar and when checked this morning its at 1.5 bar. The expansion vessel was replaced yesterday.
I have been monitoring this for weeks and everyday letting the pressure out.
Why is the air pressure in the expansion vessel going up ? is there another part to replace?

If you require any info from the boiler please let me know and I will get them for you.

Not technical at all with these things so please be gentle when replying.

 

[ShaunCorbs]

Filling loop passing ?

 

[snowhead]

The expansion vessel air pressure needs checking with no water pressure acting on it.
You can't compare the vessel air pressure if the water pressure was 1.3 then 1.8,

 

[Zishan]

ShaunCorbs - thank you for the advise. this is a internal filling loop so i have disconnected the left side of the hose (looking at front of the boiler) and i can see water dripping out, i guess its coming from main water (which is on the right side).
I will monitor this and see how it goes. I really hope this is the issue.

Snowhead - thank you for the advise. will keep that in mind.

 

[Deleted member 120897]

If you’ve had a new vessel, it doesn’t rule out a blocked communication pipe. Are you checking the digital display on the front when the pump has kicked in?

 

[Zishan]

If you’ve had a new vessel, it doesn’t rule out a blocked communication pipe. Are you checking the digital display on the front when the pump has kicked in?

Chris - can you please elaborate what should i check on the display when the pump has kicked in?

 

[EvilDrPorkChop]

Common issue with these, is it about 10 years old? The filling links start to pass.

 

[Zishan]

Common issue with these, is it about 10 years old? The filling links start to pass.

EvilDrPorkChop - I moved into this property and i was told this boiler was installed in 2018 when they did the extension. Its a pain to work on as the boiler is installed in the loft near the ground and not like shoulder height like most boilers ive seen.

Everyone - can someone explain the procedure to replace the filing loop valve on this boiler - what the procedure?

Is it called a water inlet valve that i would need to purchase?

 

[John.g]

ShaunCorbs - thank you for the advise. this is a internal filling loop so i have disconnected the left side of the hose (looking at front of the boiler) and i can see water dripping out, i guess its coming from main water (which is on the right side).
I will monitor this and see how it goes. I really hope this is the issue.

Snowhead - thank you for the advise. will keep that in mind.

If the boiler is/was off overnight for 8 hrs then the filling loop would have to pass ~ 1.25L, 156ml/hour, to increase the pressure from 1.3bar to 1.8bar assuming a 8L E.vessel.

 

[Deleted member 120897]

Chris - can you please elaborate what should i check on the display when the pump has kicked in?

I think I didn’t explain it well, you say that the pressure is increasing and wondered if you were reading the digital display, especially when the pump had kicked in.

 

[Zishan]

I think I didn’t explain it well, you say that the pressure is increasing and wondered if you were reading the digital display, especially when the pump had kicked in.

Yes so every morning i see the digital display and the pressure goes up when the pump hasnt kicked in. I make sure the boiler doesnt come on over night by lowering the temp.

John.g - the vessel in the boiler is a 10L.

 

[Zishan]

how do i replace both filling loop valves please.
Shut off main valve
Isolate the flow and return
Drain the boiler and may be some from the drain off as well.
then replace both valves

Is that correct.?

Off topic - Heating partial load setting, is that to manage to Kw of the boiler - its a 38Kw boiler but using this i can decrease the Kw to say 24? - What exactly does this function do?

thanks

 

[John.g]

Yes so every morning i see the digital display and the pressure goes up when the pump hasnt kicked in. I make sure the boiler doesnt come on over night by lowering the temp.

John.g - the vessel in the boiler is a 10L.

A 10L EV will take in 2.0L in increasing from 1.0bar to 1.5 bar overnight or 250ml/hour over 8 hours. If its still increasing with the filling loop disconnected suggest shutting off the cold mains at the boiler and open a hot tap overnight in case (hopefully not) that the plate heat exchanger is leaking mains water into the primary side and pressurizing the system.

 

[Zishan]

Just wanted to say thank you for everyone who gave advise. It was the filling loop at fault. Valve has been replaced and the pressure is now stable
...............................................

Now i have another issue - the ecotec plus 838 is not reaching its temperature which i have set to 68. Its around the 50 mark and then goes into pump over run.
Any suggestion or settings that i need to change?

 

[Deleted member 120897]

What thermostat are you using?

 

[Zishan]

What thermostat are you using?

Its a honeywell Home Thermostat. nothing speacial just to use to increase/decrease the temp. No other setting on it.

Off topic - Heating partial load setting, is that to manage to Kw of the boiler - its a 38Kw boiler but using this i can decrease the Kw to say 24? - What exactly does this function do. - -It was set to auto but i currently changed it to 24kw.

 

[John.g]

What is the exact model of that roomstat.

Range rating the boiler simply stops it from firing flat out, it will increase the time to get up to its SP temperature from cold but is better for the boiler, its a bit pointless having g a 30kw combi boiler to get a decent shower set to 30kw or Auto with a say 15kw CH demand, but itcan be left on Auto.

 

[Zishan]

What is the exact model of that roomstat.

Range rating the boiler simply stops it from firing flat out, it will increase the time to get up to its SP temperature from cold but is better for the boiler, its a bit pointless having g a 30kw combi boiler to get a decent shower set to 30kw or Auto with a say 15kw CH demand, but itcan be left on Auto.

Room Thermostat is honeywell Lyric T6R

its keeps going into Burner anti-cycling time. Which is currently set to 0 min.

 

[John.g]

The stat may be switching the boiler on/off before it reaches its (Flowtemperature) SP especially if the roomstat is at its setpoint temperature.
You can set the minimum on time to between 1 and 5 minutes, its default setting is 1 minute which may be too low, suggest 4 minutes as a start, the cycle rate defaults to 6 and is settable to 3,6,9&12, maybe try 3?. (6 is generally recommended for Gas fired and 3 for oil fired boilers)
However if its keeping very tight control of the room temperature then maybe leave as is.

 

[John.g]

Room Thermostat is honeywell Lyric T6R

its keeps going into Burner anti-cycling time. Which is currently set to 0 min.

If its going to anti cycle then its not the stat thats switching the burner/boiler off, if the stat was switching it off it would go to pump overrun.
You cant set the anti cycle time to 0, 2 is the minimum, 20 is the default but the actual anticycle time depends on the boiler flowtemp target value, if its set to the default setting of 20C then your target temp of 68C will result in a actual anticycle time of ~ 4 minutes which is reasonable, if its only set to 2 mins then the actual anticycle time is only ~ 2 minutes, a bit short IMO.
Have a look at d.001 (overrun time) and d.002 (anticycle time) and also ensure the boiler is going to anti cycle and not pump overrun.