Vailant Turbomax Restarting on hot water demand - any clues?

[advicewelcom]

Hi, I have a 20yr+ old Vaillant Turbomax VUW 282 with a magaclean (on the flow side) and connected to Hive system for a 4 bed house.

Had it serviced by British Gas engineers - but its a mixed bunch that come around and often depends on the engineer quality.

Recently had its diverter valve replaced (2018), PCB replaced (2021) and Air Pressure switch cleaned and rebuilt (2021)

At the moment its working but something weird is happening when the hot water tap is opened...

1 Central heating demand indicator comes on
2 Fan operation indicator comes on
3 Ignition indicator comes on
4 Burner indicator comes on
5 Water gets very hot within seconds
6 Boiler shuts off with Burner indicator going off
7 Water gets slightly cooler
8 Start-up cycle happens again
9 Water gets warmer slower
10 Boiler remains on second start-up and continues to provide stable hot water

Same thing happens when the central heating is on and hot water tap is opened - it cuts out the boiler on hot water demand, and then comes back on again moments later and stays on.

This can't be good for the Boiler? Its old thing, but I hear they have some life in them if looked after.

Anyone any ideas what's going on??

 

[advicewelcom]

Hi, I have a 20yr+ old Vaillant Turbomax VUW 282 with a magaclean (on the flow side) and connected to Hive system for a 4 bed house.

Had it serviced by British Gas engineers - but its a mixed bunch that come around and often depends on the engineer quality.

Recently had its diverter valve replaced (2018), PCB replaced (2021) and Air Pressure switch cleaned and rebuilt (2021)

At the moment its working but something weird is happening when the hot water tap is opened...

1 Central heating demand indicator comes on
2 Fan operation indicator comes on
3 Ignition indicator comes on
4 Burner indicator comes on
5 Water gets very hot within seconds
6 Boiler shuts off with Burner indicator going off
7 Water gets slightly cooler
8 Start-up cycle happens again
9 Water gets warmer slower
10 Boiler remains on second start-up and continues to provide stable hot water

Same thing happens when the central heating is on and hot water tap is opened - it cuts out the boiler on hot water demand, and then comes back on again moments later and stays on.

This can't be good for the Boiler? Its old thing, but I hear they have some life in them if looked after.

Anyone any ideas what's going on??

1 Hot water demand indicator comes on
2 Fan operation indicator comes on
3 Ignition indicator comes on
4 Burner indicator comes on
5 Water gets very hot within seconds
6 Boiler shuts off with Burner indicator going off
7 Water gets slightly cooler
8 Start-up cycle happens again
9 Water gets warmer slower
10 Boiler remains on second start-up and continues to provide stable hot water

*Meant to say.

 

[ShaunCorbs]

Sounds like it’s overheating

 

[advicewelcom]

Sounds like it’s overheating

... maybe.

When opening the hot water tap and keeping it running, boiler starts, then waters gets too hot in about 10s, then stops, then restarts and this time stays on with water at the right temperature for as long as the tap is on.

Does not overheat on the 2nd ignition, only the first ignition.

Surely this can't be normal hot water demand ignition cycle?

 

[ShaunCorbs]

Best to get a gas safe engineer out

 

[advicewelcom]

Best to get a gas safe engineer out

Thanks. Already got an engineer booked for Tuesday, but these British Gas Engineers are a mixed bunch. They sometimes fob you off if the boiler is actually functioning as they are only required to make sure it works - and I have a feeling that is what will happen. The central heating is working okay and only have this issue with the hot water.

So just wanted to confirm this is not how the boiler is supposed to work and therefore an issue that requires fixing. Also any pointers to what could be at fault for the overheating the first time?

 

[ShaunCorbs]

Yes there’s something wrong as it should work first time every time

 

[advicewelcom]

Yes there’s something wrong as it should work first time every time

Thanks. I just gave Valiant a call and quite surprised that they still have a lot of parts for this 20year+ boiler still available.

The tech support guy on the end of the call mentioned that it could be associated with the diverter valve or the "bundy tube" from it - with some "microswitches" top and bottom. With the possibility of them having sludge in them and needing a clean out.

... welcome to let me know if anyone has an insight on this?

 

[advicewelcom]

Just thought I would follow-up if it helps

The BG engineer checked it and did a test with the a gas meter

He said that on intial start up its around 10MB (millibars) and then it drops too 2MB and then gradually goes up to around 5MB depending on the amount of hot water demand and outside temp.

The boiler was sensing the lower water temperature request and cutting out after intial start-up as it was way too hot, compared to the low water temperatures set on the boiler. By turning up the water temperature on the boiler the cut out after start up was stopped.

Just so you know ;-)

 

[JustinD]

We seem to be having the same issue except ours cycles on and off, so far our gas engineers have changed quite a few parts like thermistor, secondary heat exchanger, primary heat exchanger and the diverter valve, it still seems to be the same so not sure what else I can ask him to check, he has stopped talking put calls as well, we may try another engineer but would like some guidance on what I could tell them to look at first, it's such a old boiler, very difficult to find someone experienced enough

thanks in advance

 

[John.g]

Just thought I would follow-up if it helps

The BG engineer checked it and did a test with the a gas meter

He said that on intial start up its around 10MB (millibars) and then it drops too 2MB and then gradually goes up to around 5MB depending on the amount of hot water demand and outside temp.

The boiler was sensing the lower water temperature request and cutting out after intial start-up as it was way too hot, compared to the low water temperatures set on the boiler. By turning up the water temperature on the boiler the cut out after start up was stopped.

Just so you know ;-)

A little bit surprised at that behavior, especially since it operates ok after the initial fire up, the minimum flow switch is set to ~ 2.5LPM which means that the HW temperature will be at a max of 41C assuming min output of 5kW and cold water at 12C, however all gas boilers fire up at ~ 60/70% output so the temperature will be far higher than this for a very short period until the boiler modulates down to maintain this 41C, if set to this, this should be catered for in the boiler logic.
You might care to measure the flowrate from this HW tap that causes the "problem", does this also happen if you open a bathroom HW tap or whatever that gives a high flowrate of say > 10LPM?.

 

[John.g]

Just thought I would follow-up if it helps

The BG engineer checked it and did a test with the a gas meter

He said that on intial start up its around 10MB (millibars) and then it drops too 2MB and then gradually goes up to around 5MB depending on the amount of hot water demand and outside temp.

The boiler was sensing the lower water temperature request and cutting out after intial start-up as it was way too hot, compared to the low water temperatures set on the boiler. By turning up the water temperature on the boiler the cut out after start up was stopped.

Just so you know ;-)

Just looking through the manual for your Vaillant Turbomax VUW 282 and I don't read anywhere where you can set the DHW temperature, CH water temperature, yes. Also its minimum output on DHW is 11.2kW and its minimum flowrate is 2.7LPM. At 11.2kW if one assumes that it trips at a DHW temp of 65C then it will require 3.0LPM from C.water at 12C so I can't see how you can have DHW temperature control, if one assumes that you have and you require a DHW temp of say 40C then the DHW flowrate would have to be a minimum of 5.7 LPM.
If you don't have DHW temperature control but increasing the CH water temperature control then either something wrong or the boiler logic has been designed this way which one might think is unusual.