Ideal Mini C24 Combi Boiler - Low DHW temp

[lyric]

Hello folks

I've just bought a house with a brand new looking Ideal Mini C24 Combi Boiler fitted. Initially, the CH wasn't properly pressurised and the radiators were full of air. But the hot water was fine. I filled a bath at full flow and had to add extra cold water to bring the temp down to confortable levels.

I bled the radiators and repressurised the system. Central Heating now works fine. Hot water never gets properly hot though. Even with the dial up fully and the tap running at low pressure it never gets above the temp that I can hold my hand in without scalding myself. Watching the burner and temperature dial I see that the boiler shuts down at around 80 degrees and restarts at about 75 degrees. The DHW temp dial doesn't seem to have any influence on anything.

I'm guessing that my initial problems with the CH and my current problems with the DHW are NOT connected and that this was a coincidence? I'm also guessing that either the DHW temp dial is faulty or there is some internal thermoswitch problem? Am I missing something obvious before I go and call out a heatingh engineer?

Many thanks for your time in answering this

Aaron

 

[chrishutt]

it never gets above the temp that I can hold my hand in without scalding myself.

It's not meant to. The DHW temp. is limited to 60 C to avoid scalding, and scale formation too.

 

[lyric]

60 degrees would scald the **** out of you!

My boiler's not getting anywhere close to that though - I definitely have a problem

 

[Agile]

Yes, you are quite right! 60*C would make you withdraw you hand pretty quickly!

Firstly, the temperature dial records the temperature of the system flow within the boiler and NOT the temperature of the water coming out!

Secondly, you may be overestimating the amount of water the boiler can heat.

Technically, it can heat 9.3 litres per minute by raising its temperature by 35 degrees.

Practically speaking if you set the boiler to 9 litres per minute then you should hardly be able to keep your hand under the hot tap.

All that assumes that the boiler is set up correctly. It probably is! Next though it assumes that all the heat is being transferred efficiently into the water. With 9 litres per minute the temperature dial should be at about 55 to 60 *C. If its significantly higher then it implies that the secondary plate heat exchanger is partly blocked with dirt from the heating system.

That fault is quite common in refurbs and new build because builders dont power flush and chemically treat the heating system properly.

The house buyers pack about 2007 may improve that problem but for the time being its "caveat exemptor". ( Latin, amo, amas, amat etc. )

Tony Glazier

 

[lyric]

Nice one Tony - thanks for getting back to me.

Your dirt blockage explanation seems to fit the events. The system worked fine initially and then deteriorated rapidly. And yes, my temp dial reads 75-80, which is much higher than your suggested 55-60 mark.

Looking through the paperwork I've found that the boiler commissioning certificate is blank, suggestive of cowboys. Also, when I bled the system it was a bit muckey initially. I couldn't tell if there was inhibitor added - does this have a notable colour or odour? The install itself looks good though - boiler has recommended clearances and they've done a nice job on routing the pipework.

If my problem really is dirt fouling the DHW heat exchanger then what's the solution? Is it too late for a power flush? What kind of money are we talking about to sort this via a Corgi engineer?

Many thanks again

Aaron

 

[Agile]

We would charge £136 inc. in London to remove the secondary heat exchanger and replace it with a recon cleaned one. This is done without any guarantee and with the warning that further dirt will be lurking in the system and will probably cause a reoccurance of the problem in about the same timescale as the appearance of the first problem.

The correct solution ( particularly if someone else is paying ) is to power flush the system for which we would charge £300 in London, this would include sorting out the secondary heat exchanger.

John the Scruff, is close to you if you could encourage him away from his computer and log fire to help you.

Tony Glazier

PS Prices do vary across the country and you should make your own enquiries in this respect.

 

[lyric]

I've just thought of something... Surely the DHW circuit is totally seperate from the CH circuit. So if there's any clogging of the secondary heat exchanger, it wouldn't be caused by a dirty CH system? This is all quite new to me so please be patient.

How do I get onto John The Scruff?

 

[Agile]

You may immagine that the CH circuit is totally seperate from the DHW but in reality there is only one primary circuit and its switched by the diverter valve motor actuator to power the central heating or the DHW according to demand with the DHW taking priority.

You could search for his postings and see if Scruffs profile includes an email or you could ensure that your own profile includes an email so that he can contact you or you could email me and I could put you in touch with him.

Tony Glazier

 

[ChrisR]

Surely the DHW circuit is totally seperate from the CH circuit.

It is, but it's the boiler-water aka primary side of the dhwhe which gets rad rust stuck to it, which gives the undesired insulation effect. Unless you have seriously hard tap water causing probs on the secondary side, in which case you get different symptoms.

 

[lyric]

Cheers for all the input guys.

Tony, I should be clickable for email now, would really appreciate John's email - I always prefer to go by recommendations.

Many thanks

Aaron

 

[lyric]

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