Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....Help!

[krammy]

Here's a challenge for anyone man enough to try and solve!

We have an 11 year old, Alpha CB24, two weeks ago, we noticed dripping from the bottom of the boiler, and the pressure gauge was well over 3bar. I then drained some water from the system, this reduced the pressure.

Everything was fine until yesterday. I woke up at 7am water all over the floor and the pressure gauge over 3bar again. So again I drained the system (down to the green zone). I turned the room thermostat down to minimum, turned off the central heating at the programmer. By 9am the pressure was back up to 3bar+............WTF?

We've had a plumber round who suggested the expansion vessel had gone and suggested we change the Pressure release valve. Does this sound reasonable? I can understand the pressure increasing while the central heating warms up, but the fact that the pressure increased even when the system was off/cold makes me wonder if the heat exchanger could be split or perforated?

Any thoughts? Thanks in advance....

 

[mcniven]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

if it expands with ch off then the expansion vessel probibly isnt it

maybe a pin hole in heat exchanger, or filling loop passing ?

 

[mcniven]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

close the cold main into boiler tonight, see if it has rose in morning

 

[krammy]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

Good idea, I will isolate the cold fill.

 

[krammy]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

if it expands with ch off then the expansion vessel probibly isnt it

maybe a pin hole in heat exchanger, or filling loop passing ?

Thanks again for your help with this, but how do I tell if its the heat exchanger or filling loop? I closed the cold fill last night and nothing has changed overnight or all day, the boiler has maintained its correct pressure, the heating is working perfectly. I have just turned on the cold fill to see if the pressure rises. Any tips how I can identify the root cause of the problem?

 

[Osp]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

Sounds as if you already have identified the root cause of the problem. The cold fill should be closed off at both ends of the loop at all times except when you are actually filling the system. The loop itself should be disconnected and hung up somewhere handy nearby. There should also be little screw-on caps to seal the filler loop attachment points.

If the filler loop is left connected, there is a danger that any small leak can bring your system up to mains pressure. As shutting off the mains has stopped the problem, it sounds like this is what has been happening on yours.

 

[krammy]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

Sounds as if you already have identified the root cause of the problem. The cold fill should be closed off at both ends of the loop at all times except when you are actually filling the system. The loop itself should be disconnected and hung up somewhere handy nearby. There should also be little screw-on caps to seal the filler loop attachment points.

If the filler loop is left connected, there is a danger that any small leak can bring your system up to mains pressure. As shutting off the mains has stopped the problem, it sounds like this is what has been happening on yours.

When I say closed the cold fill, I mean isolated the 15mm mains inlet into the boiler, so when I do this I have no DHW!
The filler loop is a flexi hose with an isolator built in (this is how I would normally top up the pressure if/when required. i.e. its always closed) this flexi hose is connected at 90degress to the main water inlet, the other end of the flexi looks like it feeds into the 22mm heating return pipe, just below the pump! So no way, at that end, of turning this off or disconnecting it!

 

[Alpha man]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

Have you had the vessel repressurised?

If you disconnect one side of the filling loop hose, then at least you will now whats what, and as long as the vessel has air in it!!

 

[krammy]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

Not that I'm aware of. How would I repressurise it?

 

[Alpha man]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

With a foot pump or similar, and it should of been checked when it was serviced.

 

[krammy]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

I guess it should be OK then, mind you its been about 18months since it was serviced!

Is there a test I can run to verify the pressure, car tyre gauge on the valve? Any idea whereabouts on the boiler the valve is, do I need to get into the boiler or is it easily accessible.

Thanks again fro taking the time to respond.

 

[jtsplumbing]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

If pressure go`s up with cold water main on, leaking into heating through heatexchanger

 

[anz]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

If pressure go`s up with cold water main on, leaking into heating through heatexchanger

I agree, won't be expansion vessel or external filling loop if you isolated cold into the boiler and left off.

 

[krammy]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

If pressure go`s up with cold water main on, leaking into heating through heatexchanger

If the heat exchanger was perforated/leaking would this be continuous or intermittent? It happened 2 weeks ago and again on Monday morning, but doesn't happen all the time, could it be temperature related? It was v cold Sunday night could the cold cause the heat exchanger to contract opening up a hole which seals itself when the temperature rises??? Might be a silly thought?

 

[Alpha man]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

If its the heat ex, then the pressure will go up constantly, if it goes up when you use HW/CH for a while, then it will be the vessel.

 

[jtsplumbing]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

Hi Alpha man, guy says pressure go`s up with everything switched off ! more your field i do-not have a lot to do with Alpha Boilers, but have had same problems on other makes of boilers, leaking through plate EX

 

[Alpha man]

Re: Alpha CB24 !!!High Pressure!!! even when the heating and DHW is turned off.....He

OP, is your mains water pressure reasonably strong?