CH always too hot

newdad · 28 Feb 2007

Hi.

I have a Baxi Combi 80 Eco - almost 5 years old. Since about a week ago the CH seems to be permanently at its hottest temp even when it is turned down to minimum. Water pressure is 1.5 when the boiler is on and 0.5 when off.

Strangely, the DHW control seems to regulate the CH temp - if I turn the DHW control down to 3/4 the gas pressure appears to drop a bit. If I turn the DHW any lower, the burner stops for 30 seconds then fires up again but switches off after another 10 seconds. It then keeps coming on and off repeatedly every 30 seconds.

I suspect the PCB may need replacing but don't want to spend close to 100 quid when I'm not even sure that's what the problem is! I have had the front off and also noticed that the AAV on the pump appears to have a leak. Could the 2 be connected?

Any help would be much appreciated.

gas4you · 28 Feb 2007

Firstly set your pressure to about 1 bar cold. This will then rise to about 2 ish when hot. (not the cure for your problem though) Sounds like a stat gone. I believe they are built in the pcb.

baxpoti · 28 Feb 2007

Start with replacing the temp sensor

Baxi part No.5108265

Its a dry pocket, so very easy to change.

newdad · 28 Feb 2007

thanks.

The safety thermostat and the temp sensor are fixed to the flow pipe. Would you recommend replacing these first then failing this replace the PCB?

[/img]

newdad · 28 Feb 2007

Thanks also to Baxpoti. Looks like we replied at the same time. I'll do just that.

Any suggestions for the leaking AAV on the pump - will this cause water pressure to drop more quickly.

baxpoti · 28 Feb 2007

newdad said:
leaking AAV on the pump - will this cause water pressure to drop more quickly.

Yes, get it repaired, as a temp fix, tighten the black knurled cap down, if it's there!

newdad · 2 Mar 2007

OK. Temp sensor replaced but no change. CH still always hot and now and again it keeps turning itself on and off every 30 seconds.

what next?

baxpoti · 2 Mar 2007

newdad said:
the gas pressure appears to drop a bit.

If this is correct, the boiler is modulating, the last resort is the PCB, I personally, have never changed a PCB on an ECO.

Your choice seems to be get a professional to look at it or change the PCB

newdad · 2 Mar 2007

I was afraid that was the case. I think I'll bite the bullet and get a pro in and have the AAV seen to at the same time.

Our old Saunier Duval gave up on us on the day my first son was born. 5 years on and the Baxi goes on the blink the same day that our second son was born - no more kids for us!!

thanks for the help.

baxpoti · 2 Mar 2007

newdad said:
Our old Saunier Duval gave up on us on the day my first son was born. 5 years on and the Baxi goes on the blink the same day that our second son was born - no more kids for us!!

Jesus, that's a spooky coincidence,

Have you called him Damien?

Only joking.

Let us know the outcome

chaps · 2 Mar 2007

newdad said:
OK. Temp sensor replaced but no change. CH still always hot and now and again it keeps turning itself on and off every 30 seconds.

what next?

you need to look at the micro switch fitted to the front of the water section. it switches from heating to hot water and chances are its knacker'd and stuck in hot water possition. pull down the control panel and its bottom left on brass lump!! move the metal tab with ya finger and see if it clicks, if it dont it needs changing. this is why the hot water thermostat knob controls heating, it thinks a tap is open and boiler runs much hotter for water.
hope this helps

newdad · 2 Mar 2007

chaps said:
you need to look at the micro switch fitted to the front of the water section. it switches from heating to hot water and chances are its knacker'd and stuck in hot water possition. pull down the control panel and its bottom left on brass lump!! move the metal tab with ya finger and see if it clicks, if it dont it needs changing. this is why the hot water thermostat knob controls heating, it thinks a tap is open and boiler runs much hotter for water.
hope this helps

The boiler had a leak a few months ago from the plunger which operates the microswitch. I fixed this with a new diaphragm kit - I've checked again and the microswitch is ok - plunger switches it on when the hot tap is opened and off when the tap is closed.

any further thoughts before I call in the pro's?

ChrisR · 3 Mar 2007

CHeck the DHW microswitch by pulling (one of )its wires off. Water ingress can make them short.

chaps · 3 Mar 2007

ChrisR said:
CHeck the DHW microswitch by pulling (one of )its wires off. Water ingress can make them short.

i would agree with that, it may be moving in the right direction at the right time but internally it may be constantly in the hot water possition, i changed one exactly like this a few months ago, it didn't click when moved by finger either, it should !!!

newdad · 3 Mar 2007

chaps said:
ChrisR said:

CHeck the DHW microswitch by pulling (one of )its wires off. Water ingress can make them short.

Click to expand...

i would agree with that, it may be moving in the right direction at the right time but internally it may be constantly in the hot water possition, i changed one exactly like this a few months ago, it didn't click when moved by finger either, it should !!!

The DHW microswitch clicks when pressed by hand then the pump starts and it fires up. It clicks again when released. I can't easily remove one of the wires to check...

The CH microswitch clicks when pressed by hand but the pump doesnt start and the boiler does not fire up. (it does when the CH is turned on and activated by the plunger.)

I have also just noticed that pressing the DHW microswitch activates the plunger in the CH which in turn operates the CH microswitch - is it supposed to do this?

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

CH always too hot

Similar threads