Potterton Performa 28 uncontrolable water temperature

[Frank247]

Hi all, first time post here

We have a Potterton Performa 28. In recent months it's had a new diverter valve and heat exchanger ( secondary). It's been working well until recently. The heating works ok, until you try and use the hot water.

If the heating is on or off, as soon as open the hot water tap the boiler fires and provides piping hot water, as in too bloody hot. Even if the temperature setting is set to it's lowest the boiler continues to heat the water until 4 lights (60 degrees) is illuminated. Even though the water temperature knob is set to the minimum.

If the heating was on when you opened the tap, once you close it again the boiler takes approximately 5 minutes to fire again.

A friend has the same boiler and tried it the above scenario and the temp lights never got beyond 40 degrees, and if the heating was on, and he closed the hot tap the boiler would fire instantly on the CH side.

So, does anyone have an idea where attention could be turned to next. Is there a common fault on these boilers that causes it to behave like this?

Thank you very much in advance.

Frank

 

[twgas]

HW thermister is the first thing I'd check.

 

[bengasman]

Did this suddenly happen all by itself, or did it gradually get worse?

 

[Frank247]

Thanks for the reply guys.

@begasman - it happened all by itself.

 

[baxpoti]

The heating works ok, until you try and use the hot water.

Yes, its a combi that has hot water preference!

the heating is on or off, as soon as open the hot water tap the boiler fires and provides piping hot water,

Your very lucky then, it normally takes at least 20 seconds

boiler continues to heat the water until 4 lights (60 degrees) is illuminated. Even though the water temperature knob is set to the minimum.

Common misunderstanding, the lights refer to the primary water only.

the heating was on when you opened the tap, once you close it again the boiler takes approximately 5 minutes to fire again.

The boiler anti-cycling feature!

friend has the same boiler and tried it the above scenario and the temp lights never got beyond 40 degrees

Oh well, you're not the only one with a faulty understanding

 

[Frank247]

Thanks for the replies guys, at the end of the day what I may have considered 'normal operation' may not have been just that.

Hope that makes sense.

baxipoti - are you suggesting that in fact the boiler is behaving as it should?

 

[petit_pablo]

Is this the performa 28 or the 28 instant? (Instant has preheat function). The temp dial on the instant only controls preheat temp not outlet temp. Its preset to achieve 55deg c

 

[baxpoti]

The temp dial on the instant only controls preheat temp not outlet temp.

Where did you get that from?

 

[Frank247]

It's just a regular performa.

The temperature knob for the HW doesn't appear to do anything.

Whereas the one for the CH will fire the boiler on and of.

 

[petit_pablo]

The temp dial on the instant only controls preheat temp not outlet temp.

Where did you get that from?

It says that in the manufacturers instructions.

 

[baxpoti]

Misinterpretation the preheat is stored primary water stored at a maximum of 82°C, depending on the 'c/h dial' setting.
This keeps the boiler hot and thus instant hot water delivery (you are not putting cold water into a cold boiler)

extract from M.I.

4. Domestic Hot Water Pre-Heat: To enjoy optimum performance of the boiler the pre-heat control should be set fully clockwise to the ON position. When there is a demand for hot water it will be supplied at approximately 65° C instantaneously.

5. Turning the control 15° clockwise from the OFF position will activate the pre-heat feature. Hot water will be supplied at approximately 35° C instantaneously.

6. To increase the temperature turn the control further clockwise. For example, when set 90° clockwise the boiler will supply hot water at approximately 44° C instantaneously. At a position 180° from clockwise (i.e. straight down) the hot water will be supplied at 52° C instantaneously.

7. When the control is set anywhere between 15° clockwise from the OFF position and the ON position, the pre-heat feature will operate.

8. With the control in the OFF position the pre-heat feature will not operate. Hot water will be supplied at approximately 50° C.