Worcester Highflow 3.5 BF- slow response to the DHW demand

[Zehroni]

Dear All,
I am just about to recharge the pressure expansion vessel on the Worcester Highflow 3.5 BF as well as replace the Auto Air Vent. To achieve both tasks I need to drain the system
However I have anther problem which I need help with please:-

The problem,
• When there is no call for DHW or CH the diverter valve is in the position that is shut to the CH passage.
• When there is a demand for DHW only the position of the diverter valve stray as it is i.e open to feed the hot water from the main Heat Exchanger to the Heat Bank where the DHW heat exchanger submerged, the boiler fires up and the main burner goes out when the required temperature of the Heat Bank reaches it’s pre set level by the DHW thermostat, That all perfect as I am expecting it.

• When the CH is switched on the diverter valve changed position and opens to the CH passage shutting the DHW passage to the Heat bank.

• Now both DHW and CH on demand, 2when calling the DHW, it starts hot using the heat stored in the Heat Bank then it get colder and colder very fast within i.e. 1 minutes, at this stage I am expecting the diverter valve to change immediately and open the Heat Bank passage i.e giving a priority the DHW,… it did not until the hot water coming from the tap becomes as cold as the water coming from the cold water tap after approximately 4-5 minutes. At this stage all the heat in the Heat Bank is dissipated.
• We got around this at the moment by switching the CH off form the programmer before going to the shower, because this would set the diverter valve to it’s normal position by opening the Heat Bank passage, hence the only priority is the DHW. When this happens the boiler fire up and keep firing as long as there is a demand for HW at the shower or any other tap in the house.

• I believe the a priority must be given to the DHW when both CH and DHW are on demand. So why the system is not behaving as I am expecting it. Could it be the DHW sensor inside the Heat Bank is not functioning properly i.e not responding fast enough to the temperature changes inside the Heat Bank. But the diverter valve changes position from CH to DHW as soon as turn DHW thermostat a small tick towards the higher side.

Any help would be highly appreciated,
Many thanks and sorry for the long story.

 

[bengasman]

Failing aavs are usually, if not always, a sign of corrosion and dirt in the system. My first guess is that your diverter is not moving freely, but is kind of sticky

 

[Zehroni]

bengasman

Many thanks for the reply, what does “aavs” mean?
The diverter valve is one year old, I replaced it with the pump and programmer last January when first moved in.

 

[Agile]

bengasman

Many thanks for the reply, what does “aavs” mean?

Look at your original posting for the clues! Dont you do simple crosswords?

The diverter valve is one year old, I replaced it with the pump and programmer last January when first moved in.

Now just why did you decide to replace the pump and diverter? Wasn't it as a result of dirt and sludge ???????

Tony

 

[Zehroni]

Tony,
I replaced them simply because they did not work, the programmer was not moving, so did the diverter valve, and the pump was making a lot of noise. This might be du to sludge, as it is an old system. I am thinking of following the instructions in the forum FAQ and flush the system using the using the main water.
I highly respect your experience and knowledge and would appreciate if you give a straight answer to eliminated more confusion.

 

[Agile]

From what you have described it sounds as if the system has or does suffer from sludge.

The basic fault does sound to be related to a slow response to the temperature fall of the store.

I suggest you measure the resistance of the sensor and then remove it and clean it of any deposits.

Tony

 

[petit_pablo]

Tony,
I I am thinking of following the instructions in the forum FAQ and flush the system using the using the main water.

Its pretty much impossible to flush a highflow due to the heat bank. The end result wouldnt be much improved

 

[Zehroni]

chaps,
Many thanks for your input and suggestions, it has conformed my suspicion, the system needs flushing and cleaning