Heatslave 15/19 erratic hot water temperature?

[Jimmyboyy]

The hot water supply from the boiler seems to be erratic. Boiling hot for a short time then like warm then hot then stone cold then luke warm.

I have recently replaced the diverter valve.
The heating works perfectly
The pressure in the boiler is fine
The cold feed pressure to the boiler is fine
The 3 bleed valves on top have been bled.

I can hear the flow switch click when I demand hot water but it doesn't always fire up right away,

My guess is the dhw thermostat.

But is it a possibility that it could be the flow switch?

Any help would be much appreciated.
Thanks.

 

[Burnerman]

On my similar 12/14 system, the burner goes through its start up procedure immediately the flow switch clicks and the burner continues to run throughout HW demand....I would be looking at the thermostat performance first- maybe by turning it up full to start with.
John

 

[Jimmyboyy]

Yea the position of the thermostat doesn't seem to make a difference and the tank is definitely not retaining the fourty odd litres of hot water it's ment too.
I have ordered the dhw thermostat, hopefully it does the job if not I think the next thing would be the flowswitch?

 

[Burnerman]

I think its worth testing the flow switch with a multi meter before replacing it.....I've never had one fail but I have had one burst
John

 

[oilhead]

I think you need to get busy with your multimeter. open up access to the PCB and run the hot tap. Meter the flow switch, then the pump. The 40 litres you refer to is not the water that comes from your taps. It is primary water that is passed through the DHW heat exchanger to heat the secondary water. If the DHW stat is faulty, then it will not switch on the burner, and the heat store may not be up to temperature.

 

[martyndc88]

Isolate the cold main going into the boiler and see if any water runs out of your hot tap. Had many of these with cross leaking showers causing this issue. Hardly ever a fault with the boiler. Id look at the plate and NRV in the plate after ruling out cross leaking

 

[Jimmyboyy]

Thanks for the advice guys, my thermostat if due to arrive monday, in the meantime I will check for cross leaking, whick I hadn't realised was a thing till now but makes alot of sence,
To clarify, I close the cold feed to the boiler but leave the mains to the house on,
If I get cold water from the hot taps then the shower mixer is crossleaking?

 

[Jimmyboyy]

And then to fix this put a non return valve onto the hot before the shower?
Or would I still have a lukewarm shower and hot taps everywhere else if I did that?

 

[martyndc88]

Thanks for the advice guys, my thermostat if due to arrive monday, in the meantime I will check for cross leaking, whick I hadn't realised was a thing till now but makes alot of sence,
To clarify, I close the cold feed to the boiler but leave the mains to the house on,
If I get cold water from the hot taps then the shower mixer is crossleaking?

Yeah try that

 

[Jimmyboyy]

So an update guys
The shower is not cross leaking, I have replaced the dhw thermostat, and the flowswitch although it seemed to be working fine, flowswitch and pump on when hot water called for, burner also firing up,,

The problem still remains tho. I am getting hot water but only about 2 litres per minute so unless you have the tap or shower on a really slow flow the water comes luke warm.

Anyone able to help me any further would be much appreciated,?

 

[oilhead]

Scaled up DHW heat exchanger

 

[Jimmyboyy]

I did think this but I live in an area with soft water and it got replaced not too long ago, my pump is also very hot when hot water is on....

 

[Burnerman]

When the hot tap is open, does the burner run continuously?
It could be an idea to remove the pump central chrome screw and see the pump is actually spinning......a small electrical screwdriver is good for this.
John

 

[Jimmyboyy]

Thanks, I will check this

 

[martyndc88]

Is your heating working