DIY Doctor UK DIY Forums

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

Hi

I believe there could be 2 things wrong.
Starting with the cheapest you could check the resistance of the c/h thermistor. This is located on the pipe on the left hand side going up into the heat exchanger. I think it is the top one. Pull off the wires and you should get a reading of 12m ohms at room temp. If you are getting an open circuit or a massive difference like 2m ohms then this is your prob. If this reads ok then it's could be the pcb

Get this checked out be a rgi as I give this info from memory of a fault I had about a year ago

Hope this helps

Paul

I've checked the switch terminal and it's ok. I presume that the switch terminal is the switch that you select either to turn the boiler off, or to have just hot water, both hot water and central heating, and the reset. Anyway, I've even opened it up, I've checked it for 240v as you said and I'm getting 240 when switched, and none when off.

There is no room stat and its looped out. The clock thing gets 240v also and you can hear it ticking and continuity is good when switched on. Also it's got 240v when on and 10v when off oddly.

Oh and of course, thanks for trying to help. :-D

I've checked the resistance. They are both cold so that it's relative. 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've checked the microswitches and they work. Also I took them off and you can see both 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.

I swapped the thermistos like you said 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 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?


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 on, let it get up to 70C or so, then turned the preheat hot water potentiometer to minimum, the heating 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 because the temp went down v quicklly and cooled it down, and the pressure went up. Still, no indicator light and no flame.

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.

I've checked the resistance. They are both cold so that it's relative. 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've checked the switch terminal and it's ok. I presume that the switch terminal is the switch that you select either to turn the boiler off, or to have just hot water, both hot water and central heating, and the reset. Anyway, I've even opened it up, I've checked it for 240v and I'm getting 240 when switched, and none when off.

There is no room stat and its looped out. The clock thing gets 240v also and you can hear it ticking and continuity is good when switched on. Also it's got 240v when on and 10v when off oddly.

I've checked the microswitches and they work. Also I took them off and you can see both 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.

I swapped the thermistos like you said 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 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?

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 on, let it get up to 70C or so, then turned the preheat hot water potentiometer to minimum, the heating 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 because the temp went down v quicklly and cooled it down, and the pressure went up. Still, no indicator light and no flame.

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.

If there's no movement on diverter pin, then yes renew the diverter.

htg

If it is the 3 way diverter valve, it takes around 1-2 hours to change it yourself.
I have just done this on my daughters baxi 105e.
Makes sure you turn off the mains boiler power, remove the front panels and then to make access 85% easier remover the left hand side panel, as you look at the front of the boiler. Turn off ALL of the isolater valves, drain down the water in the boiler, remove the plastic top section, disconnect the relevant wiring to the micro switches and the valve, making sure to make a diagram showing how they are for reconnecting, maybe take a photo of each one separately on your mobile phone, release ALL of the securing nuts, so they are hand tight, and then when you have removed the securing 'bolts/screws' from underneath the boiler housing, undo the remaining nuts to release the valve, have a bowl or an old towel ready to catch any residue water. If the valve just looks as though it may be 'gunged up' you may be able to clean it and get it working, otherwise it means a replacement, just search ebay, gumtree etc as they can be picked up very cheap, or look for a 'complete boiler' that has been removed due to an upgrade or a different fault(as I did, got the whole boiler for £20). If you have to get a replacement valve remember it will NOT come with the micro switches etc, unless its from a removed boiler then you will be able to see what is included.
Refitting is just the reverse of removal, quite simple, I used PTFE tape when reconnecting the plumbing connections and anti damp spray on the electrical connectors and bolts screws. I hope this helps you or any one else with the same issue. Paul