Bouncing needle on pressure gauge, Baxi combi 105e

[earthman]

Having a bit of trouble with this boiler, wife run the hot tap in the bath last week, complaining that the water was going from luke warm to cold, we heard the boiler making a noise and I noticed the needle on the gauge bouncing around, going into the red zone results in it shutting down/me doing a reset.

My first thought were that there could be trapped air in the system/pump, I haven't found any yet, next thought were that the mains water feed had dropped/been turned down, again not what I can see. Only other thing I can think of is the pump itself, can it not keep up with the flow required from the bath tap??.....but everything is fine when the kitchen or bathroom basins hot taps are turned.

Over the last couple of years I've fitted a new PCB and diverter valve assembly to this boiler, that did solve the problem of no hot water coming out of the taps,.....I've never had a combi boiler, would like to know even more/how they actually work. From what I gather, it's normal for the flame to extinguish once the 80 degree light has been on for a while even whilst you are calling for more hot water? Mine does this, it does fire back up, cycle on/off when the temp drops to the 70 light but by that time, the water that's in the section of pipe from the boiler to the tap isn't exactly hot. That section of pipe is longer than in most other bungalows I'd guess, our boiler is in the loft rather than kitchen.

The system is kinda currently working, wife run a bath today and said that it were OK, no boiler noise and the water were warm enough, not boiling though,.....it's always been very hot from the kitchen and basin taps though.

Any tips ideas chaps?

 

[brightspark]

does any error fault codes come up on boiler

 

[earthman]

does any error fault codes come up on boiler

The flame failure and safety thermostat did the first time, I checked the reading on that stat and it's well below 1.5ohm,.....haven't seen any error lights since.

 

[steve_s]

No disrespect but if you think the tap water is fed by the pump you really need to get a qualified gas safe engineer out to look at it

 

[earthman]

No disrespect but if you think the tap water is fed by the pump you really need to get a qualified gas safe engineer out to look at it

So the water that comes out of the taps is just mains pressure fed, fair enough,....that's all you need to have said, I'm not touching the gas section!

 

[Kayos]

Expansion vessel flat or pipe to expansion vessel blocked

Shouldn't really be poking about inside that boiler, it's not just the gas section you are not allowed to touch, its anything combustion or flue related as well

I am a gas safe registered engineer, if you want to tell me you can touch the appliance in your house I will just ignore you, its recently been to court that to be competent you have to have the qualifications, someone is in prison as he tried to argue his case in court

 

[Alan Reynolds]

I've had to fault find on boilers that "qqualified" engineers couldn't sort out so I don't hold much store in certificates.

 

[Wedg1e]

I had a Baxi Genesis 80 that gave an assortment of problems (and evidently had done for the previous owner of the house, as the bathroom ceiling directly underneath it had been replaced - the combi's in the loft). Heat exchanger seals couldn't cope with the mains pressure and kept leaking (£24 a set). The diverter valve plastic housing wasn't strong enough to resist either the water pressure or the power of the stepper motor and the motor broke off the back of the housing, so the diverter spool got stuck and wouldn't give hot water or heating, I forget which (£120 to fix). The fan failed (£80).

I won a few hundred quid on a lotto and decided the Baxi had to go so I bought a Wickes (Halstead) with more heat output than the house requires and in 15 years it's needed a new pressure relief valve as it was letting-by (£7) and a strip and clean of the CH flow switch every few years as the brass bits tarnish, preventing the switch from working. It's never been 'serviced' by anyone but me and yes, I can read the manual AND use a vacuum cleaner and a manometer, just like a real 'competent technician'. If the burn isn't quite as clean as it ought to be then send Greta round and I'll fire up my 2-stroke strimmer and light a bonfire
I installed the gas fire in the lounge as well and despite falling asleep in front of it many times I have yet to die from CO poisoning.

 

[Wedg1e]

Sorry, to give a more direct answer to the OP's problem, if the boiler has separate front panel 'stats for the DHW and CH temperatures I'd try knocking the DHW down a bit so it's not getting so hot, which makes it trip until it cools and so on. Who the hell needs 80 degree water anyway, I can't hold my hand under 50C for more than a few seconds

 

[earthman]

Expansion vessel flat or pipe to expansion vessel blocked

Shouldn't really be poking about inside that boiler, it's not just the gas section you are not allowed to touch, its anything combustion or flue related as well

I am a gas safe registered engineer, if you want to tell me you can touch the appliance in your house I will just ignore you, its recently been to court that to be competent you have to have the qualifications, someone is in prison as he tried to argue his case in court

Thanks, you talking about the inflatable bag that's positioned at the rear of the boiler?
I did connect a gauge to check the pressure the other year, it were in spec but I can check that again.

 

[earthman]

I've had to fault find on boilers that "qqualified" engineers couldn't sort out so I don't hold much store in certificates.

You were lucky that he turned up, the other year the one I phoned never even called me back,....I didn't have much choice but to fix the PCB myself.

 

[earthman]

Sorry, to give a more direct answer to the OP's problem, if the boiler has separate front panel 'stats for the DHW and CH temperatures I'd try knocking the DHW down a bit so it's not getting so hot, which makes it trip until it cools and so on. Who the hell needs 80 degree water anyway, I can't hold my hand under 50C for more than a few seconds

Thanks, recently turned that knob up a bit thinking it would help keep the bath tap hot.
That's what I don't get, why just that tap not keeping hot when the others are? They all come from the same outlet???

 

[Kayos]

I've had to fault find on boilers that "qqualified" engineers couldn't sort out so I don't hold much store in certificates.

I've never met a boiler I couldnt fix, often its doen to cost so customer decides to replace

 

[Alan Reynolds]

I've never met a boiler I couldnt fix, often its doen to cost so customer decides to replace

You're probably a proper gas engineer with a penchant for being able to think outside the box. I find that many know how things work but not how they don't work, big difference. I don't doubt that you allow nothing to beat you. Defeat is not an option to many of us

 

[sg66]

There is a filter built into the brass section under the pump, this gets blocked with crud and causes all sorts of problems it affects the circulation on the hot water shunt circuit for hot water, it does not show up in the baxi exploded diagram either.

Pressure vessel fault would show up more on heating than hot water.

Set pressure to 1.5 set heating to full if gauge goes to 3bar it's faulty or needs re charged, can also be a blockage upto the tank with crud.

As a temporary fix you can drain one of your radiators to about 1/3 this will allow for expansion.

 

[earthman]

There is a filter built into the brass section under the pump, this gets blocked with crud and causes all sorts of problems it affects the circulation on the hot water shunt circuit for hot water, it does not show up in the baxi exploded diagram either.

Pressure vessel fault would show up more on heating than hot water.

Set pressure to 1.5 set heating to full if gauge goes to 3bar it's faulty or needs re charged, can also be a blockage upto the tank with crud.

As a temporary fix you can drain one of your radiators to about 1/3 this will allow for expansion.

Thanks for those tips, I had heard about a filter but not sure where it were. If it is down to a blocked filter, why is the hot kitchen and basin taps fine? Why only the bath hot tap sometimes plays up, that's what I don't get.

 

[sg66]

If it's just one tap suspect the tap first but it shouldn't cause a boiler to need a reset and if there is a fault it should show up on the little row of led's.


Boiler doesn't care what happens to the water it just monitors flow and temperature and adjusts to match what its supposed to be doing, you can strangle a tap to get scolding water boiler will modulate gas and reduce as required.

If a thermostatic mixer goes faulty then can cause cold water to bleed through into the hot affecting not only the tap concerned but all taps, faulty mixer does not even have to be in use they can leak through internally with nothing coming out of said tap.

Much easier to diagnose being there lol

 

[earthman]

If it's just one tap suspect the tap first but it shouldn't cause a boiler to need a reset and if there is a fault it should show up on the little row of led's.


Boiler doesn't care what happens to the water it just monitors flow and temperature and adjusts to match what its supposed to be doing, you can strangle a tap to get scolding water boiler will modulate gas and reduce as required.

If a thermostatic mixer goes faulty then can cause cold water to bleed through into the hot affecting not only the tap concerned but all taps, faulty mixer does not even have to be in use they can leak through internally with nothing coming out of said tap.

Much easier to diagnose being there lol

The whole bathroom were done about 3 years ago so the tap isn't old, flow looks pretty good to me.
No warning lights currently on, like I said, wife run another bath and said it were OK,....although it's never been that great since we moved in the place. Now maybe that were down to the diverter valve sticking over time?? When I fitted the new one, no complaints on how hot the bath water got, in fact the opposite. Lol

If the mains water had been cut/worked on up the street for example, could that cause one off fault light to appear due to trapped air in the pipeline??

 

[sg66]

Unlikel,y tap would just be spitting, running a bath tap puts more stress on boiler as it's going to be the longest it runs at full power gas wise, if gauge was bouncing that's only related to the heating circuit, if the pcb is on way out and it doesn't run the pump or if pump is playing up pressure will rise quickly and it will spit water out the prv.

See how it goes