Performa eco he

[mfgs]

I am having issues with the above boiler. Basically the stat for the heating on the boiler doesn't regulate the temperature at all, even set to minimum the rads get roasting like its on max. Tested the thermistor 3.5k ohms at 60-65 degrees, so all ok. Technical advised me to change the pcb.

Changed the pcb and still have the same issue. There is only one thermistor on this boiler for hot water and heating. The hot water control thermostat on the front of the boiler is also acting like the stat for the heating side, so with the heating running if you turn the water temp down then the boiler shuts down as if you turned down the stat on the heating side. Technical passed me on to 4 different people all with no idea whats going on. Ive been advised to change the thermistor, even though the readings are fine in relation to temperatures. Also to replace the board, which is brand new. What are the odds of a brand new board having exactly the same fault as the existing one!

Anyone had this problem before? I hoping Gas Man comes to the rescue as he is the resident expert!

 

[Last Plumber]

Have you tested the wiring from PCB to Thermistor ?

 

[mfgs]

I didn't do a continuity test, but no signs of any damage and the plugs on each end look good. That wouldn't explain it though would it? Surely the fact it regulates it on the hot water control means the thermistor is doing its job? Can the wires know if its on heating or hot water?

 

[abc_plumb]

Gas valve?

 

[Last Plumber]

I didn't do a continuity test, but no signs of any damage and the plugs on each end look good. That wouldn't explain it though would it? Surely the fact it regulates it on the hot water control means the thermistor is doing its job? Can the wires know if its on heating or hot water?

I doubt it, I am clutching at straws. Just re read your original post.
I was thinking that there must be an electrical link between the two knobs e.g. In a busted plug.
There has to be a way the DHW knob is over riding the heating knob.

Is the micro switch on the diverter valve stuck ?

 

[mfgs]

What makes you think it could be the gas valve? It works fine and modulates correctly albeit from the hot water control stat.

I haven't checked the microswitch, but the boiler works ok independently for water and heating. If the microswitch was stuck wouldn't it constantly think there was demand and be firing?

 

[Last Plumber]

What makes you think it could be the gas valve? It works fine and modulates correctly albeit from the hot water control stat.

I haven't checked the microswitch, but the boiler works ok independently for water and heating. If the microswitch was stuck wouldn't it constantly think there was demand and be firing?

Yes.
You have a strange issue. I can't see two PCB's having the same issue.
Are you sure that the heating knob isn't broke and therefore not turning the potentiometer on either board

 

[mfgs]

Yeah I've checked it and also removed the knob and turned with a screwdriver to make sure. This just has me well and truly puzzled. Not got a clue what's going on and don't want to throw parts at the boiler at my customers expense but it's looking like that may be the only option.

 

[Last Plumber]

Yeah I've checked it and also removed the knob and turned with a screwdriver to make sure. This just has me well and truly puzzled. Not got a clue what's going on and don't want to throw parts at the boiler at my customers expense but it's looking like that may be the only option.

On the wiring diagram there are two green wires to DHW sensor. There is however, no sign of a DHW sensor. Some things are sent to blow your mind. If anything strikes me i'll let you know.

 

[mfgs]

I think you were on to something with the microswitch. I went a fitted a new thermistor this afternoon. Still exactly the same. Called technical and spoke to someone who seemed to know what he was talking about, said it was almost certainly the DHW microswitch. That's why the hot water thermostat is adjusting the temp for the heating as the board thinks its in hot water mode. So going to order one and fit it. The guy said he was an engineer for potterton previously and had seen this a fair few times before.

I will let you know if it works once I have fitted it.

 

[Billy Bob Bob]

No dhw NTC on this boiler,are you saying it does not modulate down at all on heating?what bp are you getting?

 

[mfgs]

It modulates but its being controlled by the hot water control on the front, the heating control does nothing.

 

[Billy Bob Bob]

It modulates but its being controlled by the hot water control on the front, the heating control does nothing.

so are you getting 10.2 mb throughout the heating cycle,does not modulate down? twice i have had the same fault but it affected dhw as well,pcb was one GV was the other ,harness between pcb and gas valve could be faulty but would affect dhw as well

 

[mfgs]

so are you getting 10.2 mb throughout the heating cycle,does not modulate down? twice i have had the same fault but it affected dhw as well,pcb was one GV was the other ,harness between pcb and gas valve could be faulty but would affect dhw as well

Yeah getting 10mb, it cuts in and out in accordance with the dhw stat on the front of the boiler. Hot water works fine. Just no control on the heating stat on the boiler. I'm getting constant continuity on the DHW microswitch blue to black which means the switch is stuck and constantly thinks its on Hot Water mode therefor overriding the central heating stat and it reacting to the hot water stat on the front of the boiler. It also cycles on and off really quickly when its cuts off with the stat.

 

[Billy Bob Bob]

Yeah getting 10mb, it cuts in and out in accordance with the dhw stat on the front of the boiler. Hot water works fine. Just no control on the heating stat on the boiler. I'm getting constant continuity on the DHW microswitch blue to black which means the switch is stuck and constantly thinks its on Hot Water mode therefor overriding the central heating stat and it reacting to the hot water stat on the front of the boiler. It also cycles on and off really quickly when its cuts off with the stat.

has there ever been a leak that you can tell of on the front dhw bush?

 

[Billy Bob Bob]

this could have got wet at some point or dhw needle is stuck ,but you would notice that strait away,for there to be continuity through this switch with no demand and the pins not sticking it can only be the switch ,normally a leaking stuffing box or bush does it in FS.440 Baxi Microswitch 5650200 248067 6.5625770

 

[kb76]

Does the boiler cycle when no demand? If microswitch is stuck it will keep firing, cut out on temperature and continue to cycle. Is it diverting correctly and not dumping heat down both. Steppers on PCB have caught me out in past too, think there's 4 on that board

 

[mfgs]

It had a leak about 3 years ago then I swapped the diaphragm etc on it to sort it. Have you ever had the microswitch stick and cause this issue?

 

[mfgs]

Does the boiler cycle when no demand? If microswitch is stuck it will keep firing, cut out on temperature and continue to cycle. Is it diverting correctly and not dumping heat down both. Steppers on PCB have caught me out in past too, think there's 4 on that board

What steppers on the board?
Seems to be diverting properly.

 

[kb76]

Sounds like microswitch is stuck, if it's the hw switch then it's dumping it down the heating when the pump starts after a demand and would cycle when should be at rest. The board is universal across a few Baxi/Potterton and has 4 steppers/switches. Just read you've changed the board and same fault so prob not that

 

[Last Plumber]

I think you were on to something with the microswitch. I went a fitted a new thermistor this afternoon. Still exactly the same. Called technical and spoke to someone who seemed to know what he was talking about, said it was almost certainly the DHW microswitch. That's why the hot water thermostat is adjusting the temp for the heating as the board thinks its in hot water mode. So going to order one and fit it. The guy said he was an engineer for potterton previously and had seen this a fair few times before.

I will let you know if it works once I have fitted it.

Yeah let me know if it is that. I'm 99% sure of it.

 

[mfgs]

Replaced the microswitch and all the cables that come with it. Problem solved. Now I need to explain to my customer what the new pcb and thermistor did haha

Thanks to everyone who helped out. Its really handy to bounce ideas of others in the trade when you are a bit stuck.