Baxi Combi 105e Instant overflowing

[zaputa]

Over the last few days my boiler, which I've had for 4 years now, has developed the latest in a long list of faults.

CH and DHW both seem to be working ok but the pressure is up to 3 bars and the Relief Valve operates constantly.

If I drain it down to 1 Bar it creeps back up and overflows once more, this happens even when the boiler is turned off.

Simple fault or is it going to cost me an arm and a leg again? Are these boilers crap or have I just been unlucky?

 

[scatmanjohn]

If you disconnect the filling loop and it still does it you will be needing a new plate heat exchanger.

 

[zaputa]

Thanks scatman I'll give that a bash.

Heat Exchanger - thats sound like an arm and a leg then.

 

[baxpoti]

Heat Exchanger - thats sound like an arm and a leg then.

PLATE heat exchanger (only cost an arm)

 

[zaputa]

Disconnected the filling loop and the problem is still there.

It now appears though that the pressure creeps up a lot quicker when I turn the manual control to demand central heating.

If I turn it to DHW only it doesn't creep up or creeps up that slowly that you cant notice (maybe need to try it overnight).

Also, strangely the radiators seem to stay hot long after I switch to DHW only. The CH neon goes out but it looks like the heating is still on! It's only when I turn to the control to the "off" position that the radiators cool down.

baxpoti - A lot more than an arm and a leg I think

 

[scatmanjohn]

Tonight turn off the boiler so it can not fire up at all.

If the pressure is still going up then its the plate heat exchanger.

If it only goes up when the heating is on, you have a different fault.

Try that first, then get back to us

 

[zaputa]

Morning scatman. Turned the boiler control to "off" position and left overnight. Pressure did not rise. In fact it dropped slightly.

This morning.

Turned control to DHW only, used hot water, everything ok. Only thing I noticed was that when I closed the hot water tap the DHW neon flashed for about 10 seconds until the "boiler fired up" neon went out. Then the DHW neon went out as well. Is this normal?

Turned control to DHW & CH. Central heating came on ok (no flashing neons) but pressure started to rise immediately. Within about 10 minutes it was nearing the "red zone". Turned it off before the PRV operated.

Turned control back to DHW only, CH neon went out, "boiler fired up" neon went out, pressure seems to be dropping slowly back to normal.

This bit is puzzling me though. The radiators are taking an age to cool down even though the boiler is not fired up and the pump is not running. They seem to cool down a lot quicker if I turn the control to "off" rather than "DHW" only.

Any help very much appreciated before I have to call out an engineer yet again.

 

[scatmanjohn]

Good morning to you sir.

It sounds like the expansion vessel needs pumping up.

You will need a foot pump.

On top of the boiler at the back is a plate held down with 4 screws, take it off.

Look for a small valve, like on a car tyre. Connect a foot pump.

Its important that the system is open to atmosphere whilst pumping up the vessel.
So the easiest way for you is to open the pressure relief valve whilst pumping it up.

Pump up to 1 bar.

Give it a go...its easy

 

[zaputa]

Forgive my ignorance but how do I open the PRV?

Also. I have a foot pump but the guage may not be accurate. Is this 1 Bar critical or just a minimum, can I overinflate?

 

[scatmanjohn]

Forgive my ignorance but how do I open the PRV?

Also. I have a foot pump but the guage may not be accurate. Is this 1 Bar critical or just a minimum, can I overinflate?

Turn it. You will feel it click back shut if you go too far.

Somewhere near 1 bar will do.

 

[zaputa]

Done that scatman.

It was easy as you said but unfortunately it hasn't worked.

Pressure still rising when CH on

 

[scatmanjohn]

When you first put the foot pump on was there any air in the vessel or did any water come out.

Are you sure you had the system "open" whilst pumping up the vessel.

 

[zaputa]

When I first connected my pump air rushed out, no water

Yes I opened the PRV valve (a red collar under the boiler) and the pressure dropped to zero.

I then pumped up the vessel, closed the PRV and opened the fill loop to repressurise.

It looks like the pressure is rising now (albeit very slowly) when the control is set to DHW only. I'm sure it has done this in the past, intermittent fault?

 

[scatmanjohn]

So i take it that the pressure is now set at 1 bar (gauge on front of boiler)

If you run the heating for 30 mins what does the pressure go up to. (its meant to rise).

 

[zaputa]

It looks like the pressure is rising now (albeit very slowly) when the control is set to DHW only. I'm sure it has done this in the past, intermittent fault?

scatman - ignore this bit. I double checked and the fill loop valve was passing water very slightly. Must have happened when I repressurised. I'm a numpty I know. It is as was, pressure is rising on CH only.

OK. I've disconnected the fill loop just be sure, reduced the pressure to 1 Bar and turned the CH on. I'll leave it for 30 mins and see what happens.