Water meter and combi boiler back pressure

[kam187]

Hello,

I have a Worchester 440cdi combi boiler which regularly dumps water out due to over pressure.

- There is 3.3 bar pressure at the property.
- There was no pressure reducing valve fitted to the inlet of the boiler.
- There was no external expansion vessel on the inlet of the boiler.

I fitted a pressure reducing valve to the inlet of the boiler. I closed the mains water, released all the pressure by running a tap. I then closed the the inlet and opened the mains, and set the valve to 1 bar.

As soon as i open the inlet to the boiler the pressure on the reducing valve starts to increase until it reaches 6 bar.

I assumed this is down to back pressure so I added a 8 litre expansion vessel pre-pressurised to 1.6 bar. Here is what i have now:

Mains in (water is metered) ----> pressure reducing valve (set to 1 bar) ----- [Expansion vessel] ------ Boiler inlet.

The same thing still happens though. As soon as i open the inlet to the boiler the pressure gauge on the reducing valve increases to 6 bar. If i run a tap it gradually reduces back down to around 1.7 bar, but when i close the tap up it goes again.

Any ideas what could be going on here?

 

[kam187]

I forgot to mention with the boiler off and the system cold the exact same thing happens. I can't understand how there could be a pressure build up of 6 bar when nothing in the system is hot or pressurised to that level. Any ideas?

 

[Scott_D]

Post some pictures

 

[kam187]

Pictures of what? Are you worried it's plumbed back to front or something?

The pressure reducing valve is from screwfix part 7978J (it won't let me post more than urls). It's fitted correctly with the flow in the right direction.

The vessel is from screwfix part 71018

 

[Scott_D]

Pics of what you have done and the boiler.

Where is it dumping water?
If you have 3.3 bar incoming how are you getting 6 bar?

 

[kam187]

Originally before I did anything, the Pressure release valve was being triggered and dumping water out.

"how are you getting 6 bar? " is the million dollar question!

I have 3.3 bar water pressure, reduced to 1 bar by the pressure reducing valve. When the all taps are off and the inlet to the boiler is opened the pressure on the pressure reducing valve guage shows 6 bar+ pressure.

So there is some back pressure from the boiler which is to be expected but not 6 bar. Why/how can this be happening?

I can post you pictures but I don't honestly understand what you are looking for. They will be of the worchster boiler and a pressure release valve :/

 

[snowhead]

I can post you pictures but I don't honestly understand what you are looking for. They will be of the worchster boiler and a pressure release valve :/

They'll confirm the layout and may give a hint as to the problem.

Is the gauge connected on the inlet or outlet side of the PRegV?

Where's it dumping water, out the boiler PReliefV?
If so what's the pressure reading on the boiler pressure gauge, normally and as it's dumping.

How long has this been happening?
Is the boiler installation new?
Has anything else changed around the time this started happening ?

 

[kam187]

They'll confirm the layout and may give a hint as to the problem.

Is the gauge connected on the inlet or outlet side of the PRegV?

Where's it dumping water, out the boiler PReliefV?
If so what's the pressure reading on the boiler pressure gauge, normally and as it's dumping.

How long has this been happening?
Is the boiler installation new?
Has anything else changed around the time this started happening ?

They'll confirm the layout and may give a hint as to the problem.

Is the gauge connected on the inlet or outlet side of the PRegV?

Where's it dumping water, out the boiler PReliefV?
If so what's the pressure reading on the boiler pressure gauge, normally and as it's dumping.

How long has this been happening?
Is the boiler installation new?
Has anything else changed around the time this started happening ?

Ok so it's two separate issues which my confusing post mixes together (sorry). Here is the timeline of events (and the problems):

Problem 1 - boiler dumping water.

Mains fed the boiler inlet directly, no expansion vessel, and no pressure control valve. The pressure on the boiler itself would go past 3 bar and the release valve would trigger and dump water. The boiler was doing this periodically for months, but otherwise working.

I found out this is likely failed or under pressured expansion vessel in the boiler.

TODAY:

I checked and topped it up to the recommended psi in the manual.

I then added in inhibitor and descaler (X100 and X200) into the fill loop. (unrelated but may have some bearing on the issue).

I DID NOT turn the boiler on to test it at this stage.

Problem 2 - over pressure on the inlet.

I then added a honeywell pressure reducing valve (A) between the mains water and the mains inlet of the boiler:

Mains (3.3 bar with water meter) ----> A ---> Boiler inlet

I then set A to 1 bar:

1) turn off mains
2) run tap to empty the boiler and inlet pipe - the pressure at A drops to 0
3) close boiler inlet.
4) Turn on mains and pressure at A is steady at 1 bar (which is what it's set at).
5) open boiler inlet, pressure at A increases till it reaches 6 bar.

The boiler is off, all water is cold, why is the pressure at A showing 6 bar?

 

[jonnyswamp]

Your incoming water main pressure (static) is 6 bar, dynamic pressure (when you run a tap) is 1.7 if I've read your post correct
The only way that would affect your central heating water pressure would be if there was a fault within the boiler, or the filling loop was slightly open
The exp vessel should be topped up when system or boiler is drained
I advise you to get a GSR in as you seem to be getting confused with the symptoms
Also you don't want to start digging too deep in the boiler without the appropriate skills and certificates

 

[kam187]

Not quite. With the inlet to the boiler shut - which isolates the boiler from the equation and the pressure reducing valve totally open the pressure is about 3.3 bar. So my mains pressure without anything open is 3.3 bar.

To make things simple:

- Pressure reducing valve totally open.
- Mains totally open.
- Inlet to the boiler closed. Boiler OFF.
- Pressure at pressure reducing valve (boiler side) is 3.3 bar

Now i open the inlet to the boiler and the pressure reducing valve gauge increases to around 6 bar.

Since the mains pressure is only 3.3 bar, the boiler must be producing 6 bar back pressure on the inlet. But how and why?

 

[Scott_D]

Not possible

 

[Dotty]

Absolutely not possible.

You need a gsr in to look at it.

Here endeth the thread.