Boiler clicking on and off

[salex]

Hi
I had a Worcester Bosch system boiler recently installed and its clicking on and off when heating up the hot water.
What occurs is that the boiler will get up to temp of 77deg then switch off for 10 seconds, the temp then drops a couple of degrees and then it will switch itself back on for a couple of seconds and so on

Not sure if its a problem with the boiler or the hot water tank thermostat
The hot water tank is a heatrae stadia megaflow

any ideas?

thanks

 

[D_Hailsham]

It's caused by the boiler thermostat turning the boiler on and off to maintain the water temperature at 77C.

The boiler will modulate down to its lowest output and then, if the water temperature still rises, it will go into on/off mode to maintain the correct temperature.

The problem occurs because the coil in the HW cylinder is not able to dissipate the heat produced by the boiler, even at lowest output.

Nothing to worry about.

 

[dcawkwell]

Something isn't right.
The coil in the megaflow should be extracting a lot more heat than that
from the heat the boiler is supplying.

My guess would be the 2 port valve to the megaflow isn't opening properly
so there is little circulation going on.

There will be a tab on the 2 port valve to the megaflow pull this across and latch it you should find the boiler goes back to heating for a longer period.

Also the cycle time on the boiler is wrong. The boiler shouldn't be relighting
for at least 2 minutes ideally 10 minutes.

 

[simond]

The heat coil in a Megaflo isnt rated above 21kw as far as I'm aware. How do you know the power output of the boiler? And as the water temp rises in cylinder the heat transfer will be less.

 

[Terry lambert]

Has the cylinder got a lockshield balancing valve fitted, cranked down too much, not allowing the heat to get away from the boiler quick enough

 

[dcawkwell]

The heat coil in a Megaflo isnt rated above 21kw as far as I'm aware. How do you know the power output of the boiler? And as the water temp rises in cylinder the heat transfer will be less.

Power output of boiler doesn't matter a brand new boiler should be modulating down to maybe 5kW. If the boiler is on and off like poster suggests something isn't right. True as temperature reaches the desired temperature this will be more often.
Even my 35kW boiler doesn't cycle above a few times before my unvented cylinder reaches temperature.

 

[salex]

thanks for all the response
I've booked another BR Gas engineers visit on the strength of it

sometimes you have to do their job for them

 

[salex]

Hi
Just to thank everyone for there assistance.
It took 3 BR engineer visits for them to admit there was a problem
Eventually I contacted worcester Bosch directly, who were very helpful indicating that the issue lay with a valve restricting the flow. Which is pretty much what everyone said on the forum
After much hand wringing Br gas are going to replace the hot water valve and much of the pipework with 28mm bore pipes. This will increase the flow , which will allow the boiler to modulate rather than turning off as the temp climbs

thanks to all

 

[mickyg]

28mm???? what on earth for? What size is the boiler?

 

[Agile]

No one can make any informed judgement without knowing the model and power of the boiler.

I would wonder if there was a wrongly set bypass valve at the boiler.

This is why a simple set of measurements of flow and return temperatures would usually immediately indicate where the fault is.

Pity so many in this industry dont like to make measurements and prefer to waffle!