DHW Cycling - What's Next?

[Christian and Beccy]

I have a Vaillant Turbomax 837e Boiler. It has been cycling fairly strongly on the Hot Water side.

I've recently replaced the DHW Heat Exchanger which appeared at first to have fixed it, but actually it hasn't. It has improved a lot, but it's still happening. Previously it would go from maximum hot to completely stone cold, but now it luckily doesn't go so cold so a shower is possible! The Heat Exchanger clearly needed doing as I've had to turn the DHW dial down massively since (previously it was on about 80% of maximum setting, now it's on about 20-30% and is delivering hotter water overall).

It's also losing a bit of pressure on the heating side, could the 2 things be related?

 

[AGAS]

how clean is your system water in ch ?

did you change the h/ex yourself ?

 

[Christian and Beccy]

The system water came out so clean. Like really really clean. Though, to be fair, it's not been in that long (12 months probably) because I cleaned the Heat Exchanger last year (obviously not very well!!). I must confess that there is no inhibitor in there currently as I have another rad to change and wanted to do that first.

Yes, I did fit the new Heat Exchanger, a genuine Valliant part.

 

[The831Bunny]

What is your hot water flow rate out of a bath tap?

The boiler will modulate & cycle with anything less than 14 L/min. You may have an Aqua Sensor problem and/or the gas burner rates are incorrectly set.

When was the boiler last serviced correctly by a Gas Safe engineer?

 

[AGAS]

The boiler will modulate & cycle with anything less than 14 L/min. You may have an Aqua Sensor problem and/or the gas burner rates are incorrectly set.

When was the boiler last serviced correctly by a Gas Safe engineer?

OP so that means you need a rgi to attend your boiler with the right equipment to test your boiler

 

[dilalio]

The boiler will modulate & cycle with anything less than 14 L/min. You may have an Aqua Sensor problem and/or the gas burner rates are incorrectly set.

When was the boiler last serviced correctly by a Gas Safe engineer?

OP so that means you need a rgi to attend your boiler with the right equipment to test your boiler

+1.
It is now beyond your remit