Water is TOO hot (Ariston Microgenus 27)

[robscheele]

This seems to be the opposite to most of the problems I have read on these pages, but our water is TOO hot!

We've got a combi boiler (Ariston Microgenus 27), and the cold water comes from the tank in the loft. This is much lower pressure than the hot water but this hasn't caused a problem before.

The hot water dial is on its minimum setting. The CH is turned down on the thermostat, but again this was the case before we started having problems.

Shower started off OK (only been in property since last December), then has been getting steadily hotter and hotter over the last 2 months. For a while running the basin hot tap helped, but even thats not doing much now. The water is coming out scalding hot.

Any ideas much appreciated - its terrible in this hot weather!

 

[ChrisR]

ALways worth measuring the hot water flow rate, say at the bath tap.

What's the shower mixer.?
It's getting unbalanced supplies (hot is higher pressure than the cold) and it might not like it. Maybe you've just been lucky up to now

Not just the shower head scaling up is it?

 

[robscheele]

It affects the water throughout the house, not just the shower head. Hot water out of the sink tap is a good indicator that the temp has got hotter - no mixers involved, straight hot and cold taps, and you can just about take the skin off your hands if you hold them under the tap!

Not sure what the mixer tap is though - nothing fancy!

The pilot flame doesn't seem to be adapting though, and I thought it was supposed to adapt as the water dispensed out of the tap?

 

[Gasguru]

The water from the mains will have got warmer over the last few months therfore the boiler wil be able to heat the water to a higher temperature - this may have some bearing on why the problem has become worse.

The minimum temperature setting of the hot hot water should produce water at around 36 degrees ie not that hot.

Run the water with the temperature setting at maximum then turn down the temperature and see if the flame height reduces.

Either way its worth ditching the cold tank and running balanced supplies to the shower.

 

[ChrisR]

And tell us the flow rates at the H ancd C kitchen taps.

 

[chrishutt]

Likely to be a faulty DHW temperature sensor. The spare part is cheap and quite easy to replace, so worth doing on a speculative basis (i.e. without being sure if that's the fault or not). With some boilers you can swap the CH and DHW sensors around as a means of testing them.

 

[robscheele]

Thanks all. I have been quoted for a new PCB by the boiler engineer as he insists that is the problem, so will ask about the temp sensors before forking out another 250 quid! He certainly hasn't mentioned anything about them to me as yet.

Cheers for the advice.

 

[ChrisR]

Here we go again. Beware "boiler engineers" who want to change pcb's without testing all other possibilities first. All too many will try different bits until it works, charging you for everything, as they guess.

But following the literature and mfrs advice can lead an engineer astray, it which makes it a bit of a lottery, with expensive parts.

Also beware boiler engineers who claim they can always make a cast iron diagnosis within ten minutes!

Some of us will only charge for faulty parts, despite what the mfrs say needs to be changed, but there can be more than one contributing to the problem. Get it clear before you proceed.

 

[Agile]

The first thing for an honest and conscientious CORGI to do is to check the gas valve settings.

Next, if anything else was necessary, he would check the sensors.

The PCB is the last part to check and costs the CORGI about £150.

Where did you find your CORGI ???

Tony Glazier


PS as a result of a few glasses of Dumisani and a blind spot of spelling, I first wrote a "conscious CORGI" !!!

 

[Softus]

The first thing for an honest and conscientious CORGI to do is to check the gas valve settings.

Nobody said that the engineer is an RGI.

Nor is there any evidence that the engineer attending is neither honest nor conscientious.

 

[Agile]

Honest to quote £250 to supply a new PCB ?

Conscientious to say its definately the PCB when he has not bothered to check the cheaper probabilities first? i.e. gas valve settings and temp sensors and APS.

Tony

 

[Softus]

Honest to quote £250 to supply a new PCB ?

Conscientious to say its definately the PCB when he has not bothered to check the cheaper probabilities first? i.e. gas valve settings and temp sensors and APS.

"only been in property since last December"

We know virtually nothing about the engineer who has quoted. Perhaps he maintained the boiler before this owner moved in? Perhaps he installed it? Maybe he knows someone who did both, or either? Maybe he's psychic?

Your technical expertise is certainly amongst the best on the forum, but it comes at a huge price - nobody beats you for arrogance and narrow-minded bigotry when it comes to matters of heating.

Let's face it Agile - everyone in the country is less honest, conscientious and professional than you claim to be.

 

[ChrisR]

rrp for the pcb is £196.366.
So £250 inc fitting shouldn't be unexpected.

 

[robscheele]

Following all your replies, I contacted a different company, recommended by the manufacturer. They came this morning and changed the temp sensor as it had, as many of you suggested, simply been clogged with limescale. That cost a fraction of a new PCB, so thank you.

Just for the record, the price I quoted of 250 was indeed 150 for the part and 90 labour. I asked Ariston if 150 was fair and they said it was, confirming the views above.

I have written to Boiler Breakdowns, who initially diagnosed the problem, expressing my disappointment at the service, and will definitely not be using them again.

It seems I would be wise to get a boiler maintenance policy, but am not sure where to look. Can you recommend a good place to start?

Thanks again to all who replied, it has saved me a fair amount of cash.

 

[ChrisR]

I'd say just find a good repairer, but I would, wouldn't I?
One serious point is that bad boiler scale wouldn't be covered by any maintenance contract.
Where in London are you?