Baxi Combi Instant 105e hot water ok but no heat?!

[Inimbrium]

Hi

I have a Baxi Combi Instant 105e.

The hot water preheat function works, and so does the normal hot water function when you turn on the tap. You can hear the pump starting up, the clicking of the diverter valve, and clicking on the spark and the lighing of the flame. It then heats up the water to the desired temperature as indicated on the temperature neons. But the central heating is dead, with no reaction from the boiler whatsoever.

So if I turn the hot water at the taps, and off by turning the preheat thermostat to zero, and turn the central heating thermostat up, and make sure the timer is on 'always on', nothing happens. The only light that is on is the power light, so no reported errors, and no sound either.

I have taken the front off and examined the circuit board and I've checked continuity for the timer and it's fine, and the timer has power also. This bioler dosn't have a roomstat.

Any ideas guys? I'm stumped.

Rafael

 

[Billy Bob Bob]

either a clock or roomstat issue

 

[Inimbrium]

either a clock or roomstat issue

Check the clock. It gets 240v, and when on it has both continuity and 240v. Definitely not the clock IMO.
There is no roomstat and it's looped out.

 

[Inimbrium]

There is no roomstat and it's looped out. There is 240v from the neutral terminal to the points before and after the roomstat connection block. Also checked it at the selector switch and at the PCB, all ok. Also checked the clock. There is 240v before and after the clock on the black wires (clock switched to always on). When clock switched off there is no voltage.

Here's some of the other stuff I've been asked to try from other forums, all with no success, but it might help:

I've checked the resistance on the CH and hot water thermistors and it's not 15k. They are both very cold so it's a fair comparison. Central Heating is at 23.83 k and hot water at 23.98 k. Also checked the safety thermostat that is just below the CH temp sensor and that measures 0.03 ohms.

I swapped the thermistors like somebody on another forum suggested and still the same problem. I was going to say that the hot water thermistor must be ok, but I don't know if it is. I turned on the preheat on minimum (turned the potentiometer just enough so that it would switch on) and the temp kept going up to 70C and probably would have gone higher if I let it, but I switched it off at the point. Surely if it's at minimum, it should have only gone up to something like 30C or 40C?

Somebody on another forum suggested I check the microswitches and they work. Also I took them off and you can see the valve shafts going in and out when calling for hot water or when preheating hot water. Both microswitches work. Also when I poke the switches the hot water comes on, but again nothing as far as CH is concerned.

Also something interesting has just happened. I've put the thermistors and everything else back how they were originally, switched the selector switch to hot water only, turned up the potentiometer to max, while the water was warming up I turned the central heating potentiometer up to max and switched the clock to always on, let it get up to 70C or so, then turned the preheat hot water potentiometer to minimum, the heating then stopped and then I turned the selector switch to both hot water and central heating. The pump kicked in, the CH light came on briefly for half a second, the pressure went up from 1 bar to 1.5 bar just like if the ch was working, and the temp went down wery quickly, so the cold water in the radiators must have been circulating through the boiler at that point because the temp went down v quicklly and cooled it down, and of course becayse the pressure went up. Still, no indicator light and no flame.

Any ideas as to what on Earth is going on?

 

[quality]

Check the micro switches on the diverter valve are operating as there is a little plastic lever which I have found in the past to have snapped and it only operates one switch

 

[Inimbrium]

One thing I noticed, it's that when taking off that black plastic thing that's on top of the diverter valve (I think it's called the operating head), the rod underneath doesn't move up or down no matter what I do. I've opened that operating head thing apart, and it's working ok. All of the parts inside work, no bits snapped off or anything and you can hear it turning and clicking.

I've checked both microswitches and they have continuity when switched, all the way to the PCB.
I've had to bring someone to look at it because it's getting pretty cold.
They said it's the diverter valve, and the diaphragm and that they need to replace the whole of the diverter valve assembly and that it would cost £250 with parts and labour.

Believe me when I say I don't like to cut corners. When I do something I'd rather pay a bit more and get it done right, you know? And I understand they need to make a living just like any of us, but, the problem is that I can't afford it. I though it would be expensive, and hence why I'm here asking for help and advice from you guys in order to try and get a fair price for the parts and labour by finding out what's wrong how much it should cost.

Would they really need to change the whole of the diverter valve part? Can't they take it apart and change the faulty part? Or if it is just the diaphragm (which they conveniently wouldn't say, and said 'it's both'). I've seen diverter valves for £87 (unsure if it's the complete assembly) and rubber diaphragms for £3 on ebay! Also he wouldn't say how much it was just for the labour, he would only give an all inclusive price.

Any suggestions would be greatly welcome.

Thanks.

 

[oldplumber]

if the diaphragm is split you only need to replace the diaphragm, not the whole assembly unless its seized up so a diaphragm costs a tenner or so plus labour say £50 to 80 depending where you live

 

[dhgas]

If the boiler fires for hot water, it is unlikely to be a diaphragm problem.

If the spindle does not move with the actuating head removed it sounds like the diverter itself is stuck in the hot water position.

 

[dmaz]

Sorry to bother you but my boiler has the same problem. What was the fault in the end ?
Cheers

 

[gas46]

hi folks sounds like diverter shuttle stuck in dhw mode so preventing flow switch on c heating from moving i would be careful messing with pcb settings though they do more than you might first think once its back up and running you would be well advised to at least gas rate it on ch and dhw