Baxi 105e Pressure Rising - Plate Heat Exchanger?

Futra · 22 Oct 2013

Hi,

we've got an old Baxi 105e, and over the last few day the pressure has been rising quite rapidly (2 bars in around 12 hours).

This happens even with the filling loop disconnected - and without the hot water or central heating being used.

I've looked through the threads on here - and I'm guessing that because the pressure rises on it's own , it's not likely to be the expansion vessel - more likely the Plate Heat Exchanger?

If this is right - will descaling and cleaning the current one fix the problem, or do I actually need a new one?

On a different subject - the 105e is at least 8 years old, and we seem to be having to spend money on it all the time now - replacing parts or maintenance. I'm wondering if it might be about time where it's no longer really cost effective to keep repairing, so does anyone have any recommendations for a replacement? We need a combi that can power a shower (Mira Combiforce 415) - so it need to be fully modulating.

Many thanks for advice on both counts!

Agile · 22 Oct 2013

All combis are fully modulating.

Plate HE must be replaced. I would be charging about £178 in local area.

Brit Gas will do a fixed price repair for perhaps about £270.

Also Baxi I expect too.

Tony

ianmcd · 22 Oct 2013

Does sound like your plate HE has perforated, if you can afford it put the money towards a new boiler you are throwing money away keeping that old boiler going they werent good when they were new never mind now

gas112 · 23 Oct 2013

Look in theinstruction book plate heat ex takes no more than 15 mins to fit start to finish and only costs around 50 INC
Keep the 105 its a really simple boiler and in the main one of the more reliable ones

AlexCarp · 23 Oct 2013

I believe it is a smaller version of my boiler, the Proforma 28. Mine is 8 years old and the DHW diaphragm and seals need changing which I am to do in a day or so. It is the first thing that has gone wrong. The boiler is very quiet compared to others. I change the inhibitor every three years so the system is clean which makes a difference and I may install a Fernox type of filter to be sure. Baxi fitted standard Italian parts used by other makes. The design is old having mechanical 3 way valves and two diaphragms. I agree with you, it "may" be worth spending out on a new boiler depending on its age. If he hasn't had problems with the 3 way valve he will have soon spending even more money.

mfarrow · 23 Oct 2013

In its defence, we've had ours for 3 years (when we moved in) and had no problems from the 12 year old beast.

Most popular are plate heat exchanger and diaphram problems. These will go; heat exchangers get clogged with crap from your system, not the boiler's fault, and the diagraphm is a cheap service item.

The PCB might be one to look out for if you have a Siemens model, identifiable by the green solder resist. These are a lot more complicated than the more basic Honeywell design which I believe is later, more reliable, and is identifiable by the clear solder resist.

Futra · 23 Oct 2013

Already had the PCB changed about 6 months ago and diaphragms have been changed a couple of months ago. Might get the HX changed anyway and see if we can get another 6 months out of it (seeing as were going to have to spend more on gas anyway)

We had been noticing recently that the radiators were getting hot when the hot water had been running for a while - would this issue be related to the HX or something else up with the diverter valve?

Thanks for the advice!

AlexCarp · 23 Oct 2013

Futra, it is best to keep it at this stage as all the main failing components have been replaced. It should last years now. It appears that the 3 way valve is not moving fully home. On my knowledge of this boiler the DHW pressure differential pin may not be moving full home. Your new diaphragm may have solved that, meaning that the next problem may be that the system is full of crud blocking the 3 way valve. The service guys here may confirm and hopefully add to this.

Put a new Fernox magnetic filter (costs about £90) on the return to the combi to catch any crud. They area easy to fit. Sentinel have brought out X-900, only to be used with filters. Put this in the system and it loosens all the crud and the filter catches it. Keep emptying the filter until all is clean. It should clean up the crud around the 3 way valve. Then pour in X-100. This filter can be used for any new combi so not a waste of money. I am going to do this on my combi. I want to reduce break down problems as much as possible and prolong the life of the system and combi.

Agile · 24 Oct 2013

Futra said:
Already had the PCB changed about 6 months ago and diaphragms have been changed a couple of months ago. Might get the HX changed anyway and see if we can get another 6 months out of it (seeing as were going to have to spend more on gas anyway)

We had been noticing recently that the radiators were getting hot when the hot water had been running for a while - would this issue be related to the HX or something else up with the diverter valve?

Thanks for the advice!

The hot rads on DHW is due to the diverter valve leaking.

But this is probably just as a result of a rather blocked plate HE.

Tony

gas112 · 24 Oct 2013

Rads getting hot when HW on is purely down to a sticking pin and a ten minute job to strip and clean and grease it no need to change entire valve as the majority of people do at a cost of £100 for valve and additional labour.

These truly are the most simple combi to repair and maintain and re parts one of cheapest also.

A filter and chemicals will in no way repair a sticking pin in the 3 way valve it needs stripping down

AlexCarp · 24 Oct 2013

gas112 said:
Rads getting hot when HW on is purely down to a sticking pin and a ten minute job to strip and clean and grease it no need to change entire valve as the majority of people do at a cost of £100 for valve and additional labour.

These truly are the most simple combi to repair and maintain and re parts one of cheapest also.

A filter and chemicals will in no way repair a sticking pin in the 3 way valve it needs stripping down

I never wrote a filter and chemicals will repair a sticking pin in a DHW pressure differential valve.

I stated that if the valves are fine (he has had both diaphragms changed) then crud from the system could be on the 3 way valve seating. X-900 and a filter should get rid of the crud, without a strip down of the valve. Sentinel state it gets rid of it all by dislodging the crud, but a filter must catch it. X-900 will clean all the system and the combi innards as well. Then when X-100 is poured in, the X-100 and filter will ensure the system stays clean and crud will not enter the combi from then onwards. As I stated the filter can be used on a future replacement boiler, so it is far from a waste of time and very definite positive all around.

This boiler may be easy to repair and the pcb has a new superior Honeywell replacement, but it does go wrong more often than others from what I gather, with minor leaks from glands, sticking pins and deterioration of the two diaphragms, although mine has been a gem, which I think is because the system is always clean and topped up with X-100.

It is nice you pinned down the problem.

gas112 · 24 Oct 2013

Love it when people believe a cleanser and filter will leave the inside of a boiler pristine .
I bet you believe in the tooth fairy and father christmas too .

AlexCarp · 25 Oct 2013

I do actually. But if you tell us a better way to keep a system clean I am all ears. I have poured in a can of X-100 into my system every three years and it is clean.

Tom1981 · 25 Oct 2013

A full strip down and clean is the only way to sort out a 3 way on these boilers, sometimes find they become jammed in place, no amount of cleaning solution will sort that little problem, it requires a good scrub or a new innards and new O-rings. The kit is cheap

A filter will help prevent more junk from getting into the appliance.

AlexCarp · 26 Oct 2013

Sentinel claim X-900 works and get rid of all crud which is caught by the filter. Has anyone used this stuff to report back?

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Baxi 105e Pressure Rising - Plate Heat Exchanger?

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