Biasi Riva Compact 32 - Luke Warm Water

[Goodfella123]

Hi,

Had this boiler fitted approx. 16 months ago.

Everything seemed fine until yesterday. Used to be able to turn the taps on full power and get scorching hot water for any given length of time.

Yesterday tried all taps in the house and each gives a burst of hot water for 10-15 seconds then runs luke warm.

Thought it may be that the heating was on at the same time, but tried with heating on and off - still a problem.

Turned-up the hot water dial on the boiler to full, but didn't sort it.

Tried doing a bit of research and have come across possible causes such as the "diaphragm" or "flow switch", but to be honest i'm a complete novice when it comes to boilers and plumbing.

If anyone can point me in the right direction or offer any advice it would be appreciated.

 

[Nixt]

Could be yet another case of debris on primary side of DHW heat exchanger preventing heat transfer thus modulating boiler whilst hot water is in full demand.

 

[Goodfella123]

Thanks Nixt,

I've tried all the taps again.

When i turn a tap on full power and full heat it goes cool, but if i reduce the power slightly the water goes really hot again.

I've read this could be a problem with the flow switch.

Is that correct, and if so, how much would a plumber charge to change the switch incl. parts?

 

[mehran]

there should be a temp guage on the front right of the contol panel. put the boiler in hot water only mode and turn a tap on at a normal use flow rate. if the guage shows the temp to be 70ish(give it a few minutae to see what temp it settles on) but the hot water is just luke warm then most likely the dhw plate heat exchanger is blocked.

 

[Goodfella123]

Mehran,

Tried that and this is what happened:

Central heating was turned on and gauge on boiler was at 70.
Switched central heating off and waited for system to cool down to 50.
Ran tap on full power, got cool water and boiler gauge didn't move.
When i reduced the power alot on the tap, the water went red hot and the gauge on the boiler moved to 70.

 

[mehran]

Your boiler is 13liters per minute (l/m) boiler. so when you run the water at 13l/m it takes what the cold inlet temp is and adds 35 degree's or deta T e.g. inlet cold is 5 degrees so the outlet will be 40 degrees at 13l/m

So if you tap are firing out more then 13l/m then it will come out cooler, less than 13l/m hotter.

Hot water will be hot in the summer cooler in the winter as the cold inlet changes.

Now the figures you give don’t point to anything with out flow rates. a clear sign is Luke warm water and that gauge showing 70ish, other than blocked dhw heat exchanger other things that can affect hot water temp is burner pressure and temp sensors

What you really need is a engineer to be standing in front of the boiler and do tests

 

[Agile]

Ideally you need to measure the DHW flow rate and then the cold water in temperature and the hot water out temperature.

Normally a blocked heat exchanger would be a gradual decline in DHW performance.

I would suggest you set the flow rate to 10 li/min and see what the temp gauge goes to first with the control knob on full and then with it on minimum.

Most engineers would probably charge about £84 plus parts as we do. You are entitled to ask about the charging policy. We do thimgs on a fixed price basis but some charge by the hour. Thats fine if they are quick but expensive if they are slow or cannot fix it!

Best to have someone who offers a no-fix no-fee !!!

Tony

 

[Goodfella123]

Thanks,

To lower the flow rate - is that the stop-tap under the sink, or would it be a tap on the pipework under the boiler?

I'll give it a try and post back after work at 6pm.

Cheers.

 

[Agile]

Er... to lower the flow rate you just dont turn the tap on full!

The flow can vary as the tap heats up so run it for a few minutes and then check it a second time.

Tony

 

[Goodfella123]

Sorry, yeah i'll try it tonight.

 

[Goodfella123]

Ran the tap on 50% power and got hot water.

Flow was constant and temperature gauge reflected temperature of water each time.

Turned the tap on full power and got cool water again.

 

[Agile]

Whats full and whats half means nothing to an engineer!

We need facts!

We need the flow rate as measured in litres per minute!!!

Tony

 

[mehran]

You have a 13l/m boiler.

So if you have 20l/m firing out your tap then it going to be cold but half that is 10 which your boiler could easily heat.

Btw I have a piece of string, how long would it be when halved?

 

[Agile]

Btw I have a piece of string, how long would it be when halved?

Thats easy!

Half as long!

Just like the OP's "half the flow"!

Tony