Turbomax VUW 242 boiler problem with hot water

[JustinD]

Hi all
So we still have this very old boiler but we have still having problems with the hot water, we have called out 3 repair engineer's, but as it's a old boiler everyone seems to guessing, so far they have changed the thermistor, secondary heat exchanger, primary heat exchanger, diverter valve also done a power flush, new radiators as well but for some reason the boiler seems to be turning off and on every few mins, and the hot water is from burning hot to warm.
Can someone guide us to what the issue could be so I can tell the repair engineer's exactly what to look at. I don't mind any experienced engineer on here who is local (west london) to me to come take a look, we have spent so much on this boiler we can't afford to get a new one at the moment. Thanks in advance

 

[ShaunCorbs]

Have they cleaned the internal filter ?

 

[JustinD]

Is that the secondary heat exchanger ? It's been replaced twice

 

[ShaunCorbs]

No there’s a filter inside the boiler

 

[JustinD]

No there’s a filter inside the boiler

Yes your right, it's on the cold water inlet, this has been checked and cleaned

 

[JustinD]

Could the modulating value need replacing ? It's so hard to understand, the engineers have replaced all the usual culprits but it still seems to be the same

 

[ShaunCorbs]

No there’s one on the heating side

 

[JustinD]

So there's one on the heating side as well as the cold water inlet as well ?

 

[ShaunCorbs]

Correct

 

[JustinD]

I'll ask them to come out Monday and check it, they have been concentrating on all the cold/hot water parts only

 

[JustinD]

Where about is this located by the way ?

 

[John.g]

I'm assuming problem on DHW side only?, can you open a (one) HW tap and measure the flowrate.
If you open all HW users does the boiler continue to fire?.
Do you have DHW temperature control as well as CH water temperature control?.

Your boiler has a max output of 24kw so if you can ensure a total flowrate of just > 6.5/7LPM then even if the boiler is not modulating the DHW temp should remain < 65C and not cause a boiler trip. If it is modulating to its minimum output of 9.6kW then a flowrate of only 2.7LPM will achieve the above.

 

[JustinD]

I'm assuming problem on DHW side only?, can you open a (one) HW tap and measure the flowrate.
If you open all HW users does the boiler continue to fire?.
Do you have DHW temperature control as well as CH water temperature control?.

Your boiler has a max output of 24kw so if you can ensure a total flowrate of just > 6.5/7LPM then even if the boiler is not modulating the DHW temp should remain < 65C and not cause a boiler trip. If it is modulating to its minimum output of 9.6kW then a flowrate of only 2.7LPM will achieve the above.

Hi the problem is the DHW side only but I've noticed it modulates when the CH is on as well, the temp hits 65c and goes off, can't understand much

 

[John.g]

Can you measure the flowrate from a HW tap, if its below 3LPM, open another HW user and measure both flow rates.