Biasi M110.32 combi DHW problem

[NGBod]

My old non condensing Biasi and rads where mains flushed and run for a month with X400 in system, then mains flushed 1 rad at a time in both directions just before the boiler was changed for a new condensing job. After fitting the new boiler the system was again flushed and X400 added. I was going to leave this in for a few weeks before flushing again and refilling with X100 but the DHW has now started playing up.
The boiler worked great for the first 10 days and then, intermittantly at first, started producing hot cold hot cold water from the taps. It is now 16 days old and barely producing any hot water after the first 30 seconds or so of turning the tap on. The heating is working fine but in DHW mode the boiler is modulating the gas to give about 30degC on the flow from the primary HE and about 25degC max out to the taps.
Yesterday I again drained the system down and mains back/ forward flushed everything and removed the plate HE and flushed that too. I saw very little evidence of blackness or bits in the water and no flow reductions.
After refilling with X100 in system and venting everything, still no change in DHW temp.
I tried testing the DHW temp probe but couldn't get a reading with the auto ranging meter I had. The fault lights only show a faulty sensor when I removed the leads from the sensor.
Is this likely to be a faulty DHW temp probe or something more complicated?
Any help appreciated.
Dave

 

[Gasguru]

If the boilers installed correctly and only a few weeks old then call out the manufactures service team.

 

[gas4you]

Possibly dv fault, but as gas says get Biasi out asap.

 

[tryitandsee]

Diverter valve not opening fully?

 

[NGBod]

Thanks for the replies guys, I assume getting Biasi out on a Sunday would be a no- go so I'd like to try and sort this myself.
The only checks I did on the DV were to check the CH flow & return pipes whilst drawing hot water and they where cold, also the pin to the micro switch was functioning correctly. I will try the other tests listed in the manual when I get home at the weekend. I assumed the DV allowed flow to either the DHW or CH, does it also shut off both if neither is selected?
Is there any point in stripping and cleaning the dv?

Dave

 

[gas4you]

Most manufacturers engineers work 363 days a year

 

[tryitandsee]

I suspect the valve will be in the rest position when in central heating mode.

It sounds like there is a restricted flow to the water/water heat exchanger.

 

[Agile]

Those are the classic symptoms of a blocked plate HE

OR

A restricted flow through the pump!

Did you check for dirt in the impeller of the pump???

How did you come to the conclusion the plate HE had no blockages?


There are two things required to diagnose the fault!

Cold resistance measurement of the TWO NTCs.

Flow and return temperatures when delivering the rated 13 li/min.

Tony

 

[NGBod]

Those are the classic symptoms of a blocked plate HE

OR

A restricted flow through the pump!

Did you check for dirt in the impeller of the pump???

How did you come to the conclusion the plate HE had no blockages?


There are two things required to diagnose the fault!

Cold resistance measurement of the TWO NTCs.

Flow and return temperatures when delivering the rated 13 li/min.

Tony

I didn't strip the pump to check for dirt but I flushed the boiler with fresh water through the connections below the boiler on the CH return and out of the CH flow pipe and pump drain with all rads shut off.
I removed the plate HE and looked in through the primary water entry and exit holes I didn't see much discolouration of the insides and then backflushed it with mains cold water through a half inch hose pipe. There was no visible difference in the flow of water coming out of the other end of the HE to what was coming out of the end of the hosepipe although I didn't actually measure the flow.
I tried measuring the cold resistance of both the NTCs but the resistance was too high for the range of my meter which just showed open circuit on both. They are not open circuit as the boiler diagnostics showed the relevant fault light as soon as I removed the plug from either of them.
I struggled to get flow and return temperatures as the boiler was modulating up and down so quickly. With the DHW temp knob on 6, for the first 30 secs the flow would go up to 40-50 degC and the hot water pipe to the tap would reach about 35 degC. I didn't measure the return temp but the pipe was holdable. After the first 30 secs the boiler starts modulating from very low to medium, judging by fan noise, and the flow temp drops and cycles every few secs between 18 - 30 degC. The return cycles between about 18 to 24 degC as does the hot water pipe to the tap. I tried turning the tap down to just above minimum flow and the boiler switched from modulating to on off mode with a 2- 3 sec cycle and slightly cooler pipes.

Dave

 

[Agile]

Unfortunately the really important info is not given there!

Its essential to know the resistance of each sensor cold ! That should be about 10k to 13k. Why is your meter not reading this? Is the meter faulty? Can you get a proper meter and measure them as this is essential for fault finding.

Its also essential to know the flow and return temperatures at the same time ideally measured with a differential temperature meter. That will indicate if there is a blockage or restricted flow.

Since its so easy to look at the pump impeller I would recommend you do that soon.

Stupid, but have you turned off blue tap and checked that nothing then comes out of the hot taps???

Has the combustion been checked using an FGA ? If so whats the CO² reading? I dont expect its associated with the problem but should have been checked on commissioning!

If the pump impeller is clear then the fault is likely to be covered by the makers guaranty.

Tony

 

[NGBod]

Unfortunately the really important info is not given there!

Its essential to know the resistance of each sensor cold ! That should be about 10k to 13k. Why is your meter not reading this? Is the meter faulty? Can you get a proper meter and measure them as this is essential for fault finding.

Its also essential to know the flow and return temperatures at the same time ideally measured with a differential temperature meter. That will indicate if there is a blockage or restricted flow.

Since its so easy to look at the pump impeller I would recommend you do that soon.

Stupid, but have you turned off blue tap and checked that nothing then comes out of the hot taps???

Has the combustion been checked using an FGA ? If so whats the CO² reading? I dont expect its associated with the problem but should have been checked on commissioning!

If the pump impeller is clear then the fault is likely to be covered by the makers guaranty.

Tony

I don't know why the meter wouldn't register the resistance but it was the only one I had that was in calibration. I've got several others (out of cal) I can try at the weekend.
I'll see if I can record and graph the flow and return temps at the weekend and I'll let you know what I find in the pump as well.
I did close the blue tap and nothing came out of the hot tap.
The supply pressure and combustion were both checked and found to be fine. CO² was 8.9/9.2 at min/max output.
Thanks for the help.
Dave

 

[Agile]

Most meters stay in cal for many years and few people bother getting them calibrated.

For boiler matters a 10% accuracy is usually quite adequate.

Rather than getting them calibrated on resistance its better to carry a selection of resistors like 100 R, 1k, 10k 50k 100k and 1 M which can be used to check the meter if there is any doubt.

A little trick when testing boilers is to connect a spare NTC loose and see how the boiler responds then.

Whilst I suspect your meter reading, if the resistance is wrong that could affect the operation of the boiler but the problem does not sound like an NTC anyway. However the NTCs should always be checked first as its so easy.

Tony

 

[NGBod]

The boiler is fixed!!
I checked the pump impeller which was mint.
Then I checked the resistance of both NTC's (with a different meter) and both read 11K6 cold.
I removed the diverter actuator which appeared to be working normally and checked the valve itself was free moving ie. I could push it easily with my little finger and it was springing back ok.
I then hooked up the temperature data logger to the flow and returns from the condensing HE and recorded the temperatures. The graph produced showed the flow temp bouncing up and down(28- 35degC) and the return temp following behind (24- 27degC). I wanted to post a jpg of the graph but it appears It's not possible.
At this point I was running out of ideas and thinking maybe it is a dodgy PCB but then checked the manual for the old boiler and found the DHW NTC was the same. I got the NTC from the old boiler and plugged it in to the DHW lead on the new boiler. Eureka! the hot water ran fine. I fitted the substitute NTC into the new boiler and logged the temperatures, they are now spot on. The flow temp climbs rapidly and levels of at 59degC and the return climbs at same speed and levels off at 40degC on setting 5 of 7. The hot water was 50 degC at the tap at 16.5 L/min flow.
I later rechecked the dodgy NTC and again got 11K6 ohms cold, checked it again and got 8K5, checked again 9K5....the resistance was jumping about all over the place, no wonder the boiler was getting confused.

Thanks for all the help.
Dave

 

[Agile]

That demonstrates the importance of checking the NTCs first although in this case it might not have indicated any problem.

Sometimes the NTCs can go o/c when they get hot. Its very rare that they give the problem you seem to have had although I have seen it once and wonder if its as a result of water inside as I cannot think of any other solution.

One nasty trick they sometimes have is to read OK with the plug off and to go o/c when you push the plug on! I have a spare plug with flying leads and croc clips as thats quicker and more reliable than trying to hold two test probes on.

At least its now sorted and was only a very minor issue ( would have been covered by the warranty though! )

Tony

 

[Agile]

I saw an NTC this afternoon which measured fine at room temp!

However at about 80°C it went nearly o/c. Actually read 1158k !

Tony