Trianco water jacket corrosion - New Oil Boiler

[triancohelp]

Hi all, looking for a bit of advice please.

Fired up my Trianco 70/90 after the summer 'break' - worked fine. Next morning opened the boiler room door - water on the floor. Stripped the unit down - 3 sides of the water jacket looked fine the other side seemed to be leaking from the welds in the middle - both recesses, somewhere around the bottom and even the weld around the water outlet pipe at the top!! Not really repairable - the unit is around 11 - 12 years old. Looked for a spare water jacket - it is a simple heat only unit - non condensing with a vertical flue. Not a lot to go wrong - apart from the water jacket. Contacted Trianco - would need to be made up specially - contact a dealer or two. Did so - quotes £650 - £850. Looked up the price of boilers - simple, heat only, non condensing (my boiler room location is in the centre of the house with no ready access to a drain and long vertical flue - not too keen on digging trenches across concrete floors or facing the prospect of condensate in my long vertical flue). Seems a limited choice of non condensing models. Worcester claim to have made none in the last 18 months, Grant only do so to special order. Can get a Trianco or a Thermsaver for around £700. Is there any great difference in simple heat only boilers - they all seem to employ a mild steel heat exchanger and a standard third party burner? Does anyone know of a source of a reasonably priced water jacket for my old Trianco - cannot believe the prices quoted for a spare part - looked at the installation manual for the most recent similar model - water jacket certainly looks quite similar.

In summary. For a new boiler of this type what would be a recommendation? Trianco, Thermsaver, Mistral, Firebird etc. Alternatively does anyone know of a sensibly priced source of Trianco water jacket spares - don't think Trianco is an option.

My heating system is unusual in that it is partially under floor (water pipes) and partially radiators. I have ambitions in the not too distant future to look at the costs and benefits of an air source heat pump for the underfloor section (RHI etc.) and leave the boiler for hot water and as a supplement - especially for the radiator section. Therefore, the cold weather notwithstanding (thank god for the log burner), I am trying to resurrect the oil burning side of the heating system without any un-necessary expenditure.

Many thanks for any help and suggestions

Regards

Graham

 

[simond]

Air Source heat pumps will offer some running cost savings when connected to underfloor heating.

However you describe a system where you are going to keep an oiler for the other areas, so you will end up buying a new oil boiler and an ASHP.

This is too capital intensive to deliver savings.

I can't see your reasoning for trying to avoid spending money on a new oil boiler if you have the considerable funds necessary to afford an ASHP. ASHPs excite people because they think they are something new and they think they will get something for nothing. They have been around for many decades and the basic technology is over 100yrs old. Used in poorly insulated houses (eg: anything older than 15 yrs) with radiators and you may not save a bean in running costs and need a 3 phase mains supply. The days where companies underspecced ASHPs and added immersion heaters to meet customer budgets are over, the new MCS rules are far more stringent.

What you need is a new condensing oil boiler. And you need to make sure the low return temps from the UFH aren't causing back end corrosion in the boiler.

Incidentally, if you buy the cheapest oil boiler on the market, would you expect it to last?

Trianco have gone bust 2 or 3 times since they made yours. They also supply cheap ASHPs if you are tempted.........

 

[triancohelp]

Hi Simon - thanks for getting back to me.

I welcome your comments re. the ASHP. I think I am trying to convince myself that the new RHI scheme will make it more viable.

I'm not really trying to buy a 'cheap' boiler as such. Just wondering out loud what the differences are between respective makes - especially as I would really prefer (need) the least complex option - standard efficiency, heat only, boilerhouse style - which seems quite hard to source these days. All boilers of this type (simple) seem to have virtually the same components (burner, heat exchanger) in a similar casing - bit of thermal protection and some exhaust baffling to manage through flow. If one make were known to have a thicker specification of steel for the water jacket construction or even a stainless option or more efficiently controlled burn processes, I think I would find that of some significance.

As must be evident - I know little about these devices and am just seeking some information from those that have much more knowledge and experience.

Interested in your comment re. the dependancy of return flow temperature with regard to water jacket corrosion. Could you kindly outline the corrosion mechanism at work here please for me. I had mistakenly assumed that corrosion was dependant only on dissolved O2 content and dissolved salts (impacting PH). In the presence of O2 I can see how temperature could influence corrosion rates - however I would have thought that the higher the temperature the more potential corrosion rather than the lower.

Once again many thanks for your help.

Regards

Graham

 

[Boilerman2]

Here's my thoughts:

if you put a new boiler in it would have to be condensing, the arguments you put forward for not doing so would not satisfy LABC, a Condensate pump could be installed to pump the condensate away.

However if you get TRIANCO to make a replacement Heat Exchanger, you could fit that because you would be seen to be repairing an existing boiler because a Heat Exchanger is just another spare part you are fitting

That would be your best route to avoid fitting a steamer whilst remaining compliant with building regs!

 

[Boilerman2]

To answer your question regarding low water temperature and corrosion -
it is down to the "Acid Dew Point" this is the temperature at which the combustion gasses start to condense (turn to water) combustion gasses contain a lot of Sulphur, which when wet becomes our old friend "Sulphuric Acid" and this is what does for many a steel boiler.

The boiler flow temperature should be sufficiently high to keep the Return water temperature above 55'c (Acid Dew point is 51'c)

 

[triancohelp]

Many thanks for getting back to me.

Not hugely keen on asking Trianco to make me a new water jacket - the boiler has not exactly been a paragon of reliability over the years. Suffice to say I have ended up finding out more about how it works that I ever intended to. Please don't interpret that as damning everything that Trianco do or have done - I'm working from a very small sample (one) and, in my experience, they have in the past provided good warranty support. I'll have a look at some devices for pumping condensate from the boiler room - problem is it is in the centre of the building and the nearest drain is across a room in the house - in any direction. Can't go under the floor - piped under floor heating with concrete screed. So it looks like a ceiling demolition assessment - I'm going to be popular.

I understand your point regarding the sulphur content of exhaust gases and its conversion to sulphuric acid as it precipitates, however I thought that simond was talking about the temperature of the return from the under floor heating system.

Quote 'And you need to make sure the low return temps from the UFH aren't causing back end corrosion in the boiler'.

That was the phrase that confused me. I don't understand what chemical mechanism would cause this effect.

Best regards and thanks for your time.

 

[oilhead]

Low return temperature causes ordinary condensation around the return port (like you get on metal windowframes) not to be confused with flue condense.
This causes corrosion in time, and has rotted many a steel boiler. Oil boilers seem to suffer most because they are often oversized and tend to short cycle as the boiler cannot dissipate all the heat produced.

 

[triancohelp]

Hi, Thanks Oilhead.

That does make sense. I assume if the return flow cools one side of the boiler to such an extent that condensate forms - this could include chemicals from nearby exhaust gases - including sulphurous oxides and sulphur dioxide?? Do boiler manufactures make any attempt at surface protection to cope with these cases?

I have underfloor heating - with a large volume of fluid within the underfloor pipes. This means that the temperature differential between supply and return is always much less that in the case of a low volume (relatively)/high heat dispersion radiator system. Consequently I probably have low return temperatures for a period until the overall mass off circulating water reaches a certain 'moving difference' level relative to supply and return. Not sure I can really do much about this but would welcome any suggestions. Stainless Steel??

Best Regards and thanks

 

[oilhead]

I would hope it doesn't mix with exhaust gases!!!!! If so, then corrosion is the least of your worries. It is just plain straightforward rust, which starts in unprotected areas such as the return thread.
Your UFH should have a mixing valve to control the circuit flow so that the return should be hot enough to avoid problems.