Baxi 105e replacing plate heat exchanger

[rizanx01]

Hi can anyone give me a basic step by step instruction on replacing the plate heat exchanger. The fault is hot water running hot then cold and hot again with the boiler cycling on and off. DHW fine. All the research I have done points to this being sludged up. Have seen the part for around £50. A couple of questions - do I need to order any extra o rings etc. And also what is the best way to treat the water system after I have replaced it.
Any thoughts would be appreciated but a step by step guide would be great.
Also, does anyone know the correct technique for diagnosing this - I find it a bit baffling and have tried to understand the theory behind how it works. Managed to confirm the thermistor is operating correctly but no other tests to prove it.
Help.

 

[ianmcd]

its easy enough to change but you will need a set of seals (4) before you start you cant reuse the old ones

 

[rizanx01]

Thanks Ianmcd - I wondered if I needed to order them. Just in terms of the diagnosis - when I call for hot water the boiler pressure increases slightly - is that normal?

 

[gas112]

No need to replace it just clean it out with brick acid 5 minutes to remove 20 mins of brick acid 5 mins to refit.
I would not bother with new seals about a fiver each and 4 req had loads an loads of 105 plates out and only ever had 1 seal weep afterwards

 

[rizanx01]

No need to replace it just clean it out with brick acid 5 minutes to remove 20 mins of brick acid 5 mins to refit.
I would not bother with new seals about a fiver each and 4 req had loads an loads of 105 plates out and only ever had 1 seal weep afterwards

Thanks - would you add anything to the sytem afterwards, new houses etc so no idea if there is inhibitor etc in the sytem - what do you recommend. Cheers

 

[TheGasMan26]

Firstly if you havnt got the manual, get it, that has great step by step instructions, its pretty logical as its held in by 2 x bolts/screws, youve obviously first gotta drain the boiler & isolate the water going in to the boiler.

For a cleaning agent its easiest to go into a plumbing merchants and buy either(in order i prefer) FX2, DS40, X800, also get some silicone grease while your there, when your hex is removed you pour your agent into the holes followed by some boiling water from the kettle then leave it for 10 mins, then flush it through very thoroughly with fresh water and inspect visually, if youv used FX2 the surfaces inside will be clean & silvery.

The 4 seals/washers can be re-used if in good condition, if looking rough clean with a bit of oil as this makes the dirt come loose and also makes the rubber nice and moist/flexible again, liberally smear with silicone grease and very importantly clean all mating surfaces on the hex and on the boiler, then put the seals back in the opposite way round to when you took them out.

Refill the system with some inhibitor in and ensure you get all air out via the bleed points/aavs, if your issue is a blocked hex then you should ideally be fitting a system filter to prevent this reoccurring.

good luck.

 

[rizanx01]

Thanks gasman - perfect response, understand totally now what to do. Got the manual and it looks straightforward but great advice.

Thanks all - I will let you know how I get on

 

[gas112]

cementone brick acid avialable in any builders merchants and at £7 a litre cheaper than products from plumbers merchants or spirit of salts if avialable from chemist or hardware shops even cheaper

 

[Agile]

I dont know what that brick acid is.

I always thought it was sulphuric which should not be used for lime scale. But others have said its HCl which is OK although a bit harsh if not diluted to about 10%.

Spirits of salt is about £3 for 1/2 litre but not very widely stocked.

Tony

 

[gas112]

You have already been answered several times what brick acid is Agile obviously it takes some sinking in with you , must be your age .
Perhaps if someone in a sari told you you may take more notice

 

[joe-90]

Brick acid, spirits of salt, descaler etc are all hydrochloric acid. Sometimes called muriatic acid too but not seen that name in years.

 

[rizanx01]

Thanks everyone for the advice here - havn't had time to get anything to descale the HE but have removed and thoroughly flushed it through with water lots of stuff came out, and with flushing for about 10 mins and some gentle tapping manged to remove lots of black scale - hot water restored and working fine. I want to clean properly and fill the system with some sort of inhibitor and flush the system. Have seen power flushes etc. and the magnetic devices, looks v expensive. Can anyone recommend the best DIY process for treating and cleaning the system.
Thanks again all
Geoff

 

[joe-90]

Screwfix do some dead cheap stuff under their 'No Nonsense' brand and I've been wondering if it's any good. Maybe one of the gas bods can tell us.