Ferroli F30 DHW only lukewarm

[ianshearer]

I have a Ferroli F30 combi, the CH seems ok as the radiators get hot, but the DHW only runs lukewarm.

I have checked that the light for DHW comes on, so the flow sensor seems to be working, and the temp sensor measures 8.5k when mildly warm, which seems about right, the manual mentions 10K at 25C.
The CH sensor measures the same.
The boiler fires up, but I cant tell if it is modulating, the flame base bright blue bits are about 5 mm high and don't seem to vary.
I'm an electronics/ computer guy, so I'm not touching the gas. I suspect it may need the gas inlet and max/min pressures tested?
Any suggestions gratefully received, and can anyone sugest a heating engineer in the Glasgow area?

 

[bengasman]

Is it continuously not hot enough, or does it go hot cold hot?
You need to measure the ntc at 3 different temperatures to check that the curve is right, one measurement does not mean a lot.
Run the tap full open, at 6 litres per minute and at 3/min, see if there is any difference.

 

[ianshearer]

It is continuously lukewarm when it is just the DHW. If the CH is demanding heat when the water is put on, it can be hot for 10 secs, but this is due to standing water in the Ferroli fancy heat exchanger, I think (no diverter valve on this boiler)
Good point on the ntc, I will try to get a reading when the outlet pipe is hot.
Could anyone tell me what the voltages across the modulating coils on the gas valve should be?

 

[ianshearer]

Thanks, bengasman I shall go round tomorrow evening ( my son's flat)armed with a 20k resistor and a 20k trimpot, so I can be any temperature I want, and see if that varies the DHW temp at different flow rates.
Other postings had similar problems caused by a high resistance APS microswitch- must upset the pcb somehow- so I will check that. I will also remove the PCB, which will reseat all the edge connectors (one was so tight when I tried to reseat it lat time I couldn't get it off) I will check for dry joints, open cct trimmers and jumper settings.
If it is still not modulating then I will have to find a boiler engineer who can check all the gas pressures. I can get a MF03 pcb, for £65, but I will still need a gas engineer to set it up

 

[Trundles Tricks]

I know that this seems a touch simplistic but I had a call yesterday to one of these boilers with exactly the same fault description given over the phone (without the resistance stuff)



And was due to no pressure in the system, CH worked a treat but lukewarm HW, repressurised and away she went good as new.



Only mention it just in case you haven't checked the pressure before delving into the boiler innards.

 

[ianshearer]

That's interesting, I would have expected low pressure in the CH loop would have affected the CH, or tripped the pressure switch and stoped everything.
Have to wonder what is going on for that to effect the DHW?
I will check the low pressure switch, although there is no warning light, and the pressure gauge is actually showing too high, nearly 3 bar, and the release valve has bled off recently

 

[ianshearer]

Had a 4 hour session with my beloved boiler last night:-
I have checked the APS, safety stat, low water pressure switch and the CH limit stat.
I have removed and checked the PCB for visual damage or dry joints.
I have replaced the DHW flow temp sensor with a 20K ohm variable resistor, and with it set to 20K ( 10C ) taken the following
measurements.



Modulating coils
CH Temp C MV1/MV2 MV3/MV4
IN 42 100v 20.6v
OUT 51
Demand 60
(front panel control)

DHW Temp C MV1/MV2 MV3/MV4
IN 10 109v 27.8v
OUT 30
Demand max
(front panel control)

From reading the MI, P3 on the PCB is used to force the boiler to min and max flame, to allow pressure setting adjustment.
Moving this between min and max does show a slight visual difference to the burner flame height, but I do not know if this is enough or not- I suspect not.
My suspicion is the gas pressures are too low,possibly because the input pressure is low. There is a 14 meter run from the gas meter to the boiler, it is in 15mm copper where I can see it, don't know what it is under the floor.
I cant find any other explanation for a temp lift of only 20C on the DHW.
I don't have a flow rate, but turning the tap down till the boiler cuts out only gets 30C

Any observations welcomed

 

[bengasman]

i take it that "30" in the model name stands for 30 kW, if that is correct, 15mm is well undersized. how much of that is there?

 

[ianshearer]

bengasman, I think you have put your finger on it, the helpfull guy a Ferroli replied to my email:-

"14 metres of 15mm tube will pass slightly over 1m3/hr. To operate correctly the F30 requires 3.5m3/hr."
one third of the gas the boiler needs would explain how it is behaving,
Thanks to all who responded

 

[Agile]

Your initial posting implied that it was a fault that had occured and not a normal condition for the installation.

I hope that you dont approach electronics faults in the same way!

Tony

 

[bengasman]

this is the problem with deduction from a distance.
had i been onsite, the fault finding would have taken less then a minute.

 

[ianshearer]

Geeze guys,
I implied it was a fault because that is what I thought it was. The boiler is in a flat my son lives in, he had been there for 6 months before he mentioned the hot water in the kitchen ran cold sometimes. With the CH on (which gets hot fine) you get a big slug of hot water from the heat exchanger. In the summer the incoming water is much warmer so the 20C lift in temp gives your warmer water.
They have an electric shower, so don't run lots of hot.
I therefore thought I was looking at an intermittent fault that had gone solid.

If I was a gas guy I would have a nanometer, but I haven't, so I couldn't do the obvious thing and check the gas pressure, I had to use a process of elimination. Also I don't spend my days looking at boilers so didn't know what a 30kw flame hight should look like.

I don't think I did to badly, got there in the end with your help.

 

[Agile]

If I was a gas guy I would have a nanometer, but I haven't, so I couldn't do the obvious thing and check the gas pressure, I had to use a process of elimination. .

A "nanometer" is 10 -9 m that is a (very small) unit of distance!

As an electronics engineer you should be familiar with the specification for the wavelength of the output of infrared LEDs for example as 800 nanometers.

Even if you cannot measure gas pressure there is another way that you could have measured the power input to the boiler without needing any CORGi qualification or even a manometer.

You could have made a timed measurement of gas consumption at the gas meter using the dial and your stopwatch and then calculated the power based on the calorific value of the gas supplied.

That would have indicated that the power input was too low.

You could also have calculated the pipe resistance of the undersized 15 mm supply pipe!

Tony

 

[ianshearer]

I don't know for sure yet that the pipe is 15mm all the way from the meter, it's an assumption at the moment that fits the observable facts.
If I understand things correctly, the gas valve max pressure set to low would give the same symptoms of too low a gas consumption, so no point me finding out how too work the maths on gas consumption.

It obviously is burning gas at too low a rate as it isn't heating the water.
As has been kindly pointed out, by not being a professional I have wasted enough time already.
I did enjoy gaining a better understanding of how the boiler functions, so not a complete waste of time.

So I will need the services of a CORGI registered Engineer with a Manometer

 

[cowboyplumber]

I thought a nanometer was used to measure grandmothers...