Baxi Combi Instant 105e DHW problem

dave1664 · 5 Nov 2008

Fro reading the forums it seems that Tony has had a lot to do with these awful boilers. My problem is very common. These boilers work a treat on Central heating but try getting any consistent DHW from it!!
The boiler operates as it should apart from the preheat function.
Turn hot tap on - get warmish water out (Pre heat turned 3/4 on).
Turn hot tap off - boiler shuts off straightaway (no flashing green tap neon). I thought it should always go into preheat mode once a demand for hot water has been called?
I have changed both CH and DHW diaphrams, microswitch loom, and both temperature sensors. system pressure is fairly steady at about 1.5 bar. All the pins seem to be operating ok on the diverter and I am getting 230V to the diverter motor.
One other thing I have read that with zero system pressure, the expansion vessel should be charged to 1 bar? When I tried pumping it up after I changed CH diaphram I could not get any air pressure into it untill after I had repressurised the primary loop.
I am now left with thinking I may need a new expansion vessel or even the heat exchanger could be silted up? Finally could someone advise me that I am ok (legally) to work on the water side? I have not touched anything to do with the gas side. Many thanks - Dave.

Deleted member 105431 · 5 Nov 2008

thats Potterton/Baxi (POXI) for you I'm afraid. It is a grey area whether you are allowed to "work" on a gas appliance even on the water side although most ppl will say it's ok.

Your diy efforts don't seem to be getting anywhere, why don't you call a skilled professional in and get a fixed price repair from Baxi?

dave1664 · 5 Nov 2008

I already did. Called Heateam.When the engineer came out he said it needed a new diverter valve and left us without any DHW and said it would take over a week to order the part.. In frustration I looked into it myself and replaced the parts listed. It cured the problem at first but now back to only warm hot water.
If an engineer could definetely say what the problem is and he could cure it I would happily pay. I seem to be going around in circles with this. Do you suggest I call out Heateam again - tell them what I have done so far and let them take it from there? I did not want to take out a years contract as I am moving house but would like to get the problem sorted.

dave1664 · 5 Nov 2008

Forgot to mention Baxi do not do fixed price repairs. They now only do a I year maintenance contract @ £300

Deleted member 105431 · 5 Nov 2008

dave1664 said:
Forgot to mention Baxi do not do fixed price repairs. They now only do a I year maintenance contract @ £300

£300 or a new boiler @ £1500 approx. If you sell the house pass contract onto new owner as a bonus. If you pay the 300 though make sure they get it working perfectly or keep calling them back again and again. . . .

Agile · 5 Nov 2008

I think that British Gas do a repair followed by a one year contract for about £230.

In this world if you want it fixed and cannot do it yourself then you have got to pay.

I still dont know how you seem to have had Heateam out and its not been repaired or paid for.

Tony

dave1664 · 5 Nov 2008

The reason is because I made a complaint after they failed to repair in sufficient time. It is still on going and my boiler is still not working correctly.
Is this website just about proffesionals trying to talk ametuers out of attempting any repairs? Dave.

spacethegas · 5 Nov 2008

dave1664 said:
Is this website just about proffesionals trying to talk amateurs out of attempting any repairs? Dave.

that attitude is not going to help you.

you are receiving advice. anyone who responds is doing so in order to help you. it is a forum after all.

no one is being paid to give you technical advice. perhaps you would be happier ringing the baxipot technical helpline 08706060780.

dave1664 · 5 Nov 2008

Point taken. Thanks for all your help anyway.

spacethegas · 5 Nov 2008

from what i understand the expansion vessel accommodates the heated primary water used as dhw preheat.

i don't quite understand the problem you had repressurising the vessel, explain please.

with the boiler empty of primary water & boiler drain open it should be no problem to charge it to 0.5 bar (as per mi) not 1 bar.

if the preheat does not start the mi suggest 'check continuity of loop on A10 connector'. i assume thats on pcb. then it says new pcb.

dave1664 · 5 Nov 2008

The problem I had repressurizing the vessel was that with the system drained it seemed as though the air being pumped in was not doing anything. I gave it several pumps from the foot pump but did not feel any resistance at all. Would this take long with the system completely empty? I then filled the system. Once all the air had expelled out of the air vent I then checked the vessel pressure. It is now showing about 0.5 bar on the foot pump gauge. All this occurred after I had changed the CH diaphram. I think you are right I need a skilled person here to take a look - but who? Baxi said it is the diverter valve at fault then disappeared, leaving me in limbo. Why would it be the diverter valve when the boiler is working perfectly apart from only giving warm water instead of hot?

I have also since noticed two other things:

1, If using the shower upstairs (mixer) the water is warm enough for showering. The boiler then shuts down completely after shower is turned off. (no pre heat mode)

2, If tap is turned on and off downstairs for a short time the boiler seems to get 'stuck' in preheat mode (flashing neon tap). Sometimes for several minutes.

Any thoughts? If you think it is anything sinister I WILL get proffesional help. Although as an electrician I am more than capable of changing a circuit board if you think it could be that. atb Dave.

spacethegas · 6 Nov 2008

your expansion vessel is almost empty to start with.

with boiler empty & drain open (im guessing here, as i've never counted) your going to need to pump it 30-50 times.

Agile · 6 Nov 2008

No....

If the foot pump just pumps without increasing the pressure then the EXV diaphragm is holed!

This EXV usually fails every two years. Its a good boiler to keep on a maintenance contract.

Presumably if you add an external EXV to the system then the boiler will work fine and have greater thermal storage for the DHW?

Tony

dave1664 · 6 Nov 2008

But if the EXV diaphram is holed why does it have air pressure in it when charged with water at normal operating pressure? Tx Dave.

spacethegas · 6 Nov 2008

check it.

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Baxi Combi Instant 105e DHW problem

Deleted member 105431

Deleted member 105431

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