worcester Greenstar I28 junior hot water controls missing

[Kirito]

we have the green star i28 junior combi boiler, when we use tap water or shower the water temp is very hot but flow ok but after some time its gets cold and then hot water start again, it is almost like it runs for a min and then takes 15 second break.


I want to do two things, 1) decrease the tap water temperature
2)somehow stop the cold water that comes in between hot water.

The problem is there is no controls for the tap water only for the central heating.
The boiler was recently serviced by the british gas before we moved in.

we have a normal thermostat to control central heating by the stairs but that doesn't have controls for the water as well, I have attached the receiver and thermostat along with boiler photo.

how do we control the tap water as the central heating have no problem at all just water water is too hot and stop for few second in between using it .

 

[DP]

You system has not been cleaned, now you have sediment in the hot water heat exchanger. Boiler electronics are keeping the boiler in check because the heated water cannot cannot be transferred in required quantity to the hot water heat exchanger due to sediment now clogging the plates.

Having a hot water control would not solve your problem. Replacement heat exchanger and cleaning the system would be the way forward.

 

[oldbuffer]

1. Your boiler has a set hot water (Domestic Hot Water (DHW)) of 55 degrees when it is working correctly. It cannot be altered.
2. You could fit a Thermostatic Mixing Valve (TMV) at each hot water outlet to reduce the temperature. These work by mixing cold water with the incoming hot and thermostatically controlling the temperature of the outgoing hot to the appliance. They are between £30 and £60 each, but can be quite difficult to fit depending on access. I would budget a couple of hours to fit one. They are meant to be serviced annually.
3. The hot - cold - hot - cold problem you describe could be one of a number of things. The most likely are:
3a. The secondary heat exchanger in the boiler needs cleaning or replacing. Replacing is often cheaper than cleaning.
3b. The flow sensor in the boiler is faulty.
3c. There is a problem with a mixer tap allowing cold water to overpower the hot. Least likely of the above in my opinion.

 

[Kirito]

You system has not been cleaned, now you have sediment in the hot water heat exchanger. Boiler electronics are keeping the boiler in check because the heated water cannot cannot be transferred in required quantity to the hot water heat exchanger due to sediment now clogging the plates.

Having a hot water control would not solve your problem. Replacement heat exchanger and cleaning the system would be the way forward.

thanks for the info, do you know how something like this normally cost?
can it be done by avg person or does it require a engineer

 

[DP]

A heating engineer who mainly does servicing and breakdowns.
Might be an idea to install Addey Megnaclean. I like this brand as it is best at intercepting the sediment before it gets into the boiler like it has done now
Putting your location can help recommend some regulars who do this type of work day in day out.

You could call Worcester and ask for a fixed price repair.

 

[Kirito]

A heating engineer who mainly does servicing and breakdowns.
Might be an idea to install Addey Megnaclean. I like this brand as it is best at intercepting the sediment before it gets into the boiler like it has done now
Putting your location can help recommend some regulars who do this type of work day in day out.

You could call Worcester and ask for a fixed price repair.

I am in Manchester so if you know anyone good plz recommend

 

[ianmcd]

Go for the worcester fixed price repair, is about £270 but covers labour and parts and you get a warranty