Shower causing boiler to cycle heating

[Darkmagi666]

I've just had my boiler's diverter valve changed & a new pump fitted after it died while the plumber did the repair to the diverter ? It's a Linea 28.

Anyway the the boiler is running ok now, The hot water is staying constant at all the taps with the kitchen sink running at 11 litres a minute at 52c but the strange thing is when we use the shower upstairs which we run at about 9 litres a minute the temp goes up to 67c then the boiler cuts out & the temp drops to about 42c then the boiler kicks in & does the same thing again, I called the engineer but he cant get back out for a week & I would love an idea as to what could be wrong before he dies come back. TIA

 

[ianmcd]

OK run the shower and go to the boiler, locate the inlet valve to the cold water, a three way valve with a black handle, furthest right hand side pipe under the boiler, the display when the HW is running will be the temp of the DHW, as soon as the burner closes down turn the valve handle to the 9 oclock position and the display number will change, come back and tell us what the new display number is

 

[Darkmagi666]

I ran the shower which was going up to 52c then dropping to about 44c when the boiler cut off & I turned the handle the temp reading was at 60c.

 

[ianmcd]

That is normal but the boiler should modulate down , not cut out, this can be caused by a few things but unless its the shower itself , the checks to be done inside the boiler are not DIY, if it is only doing it on the one outlet I would say that is the problem, try running the shower and open the HW tap in the same room at the same time and see if the boiler still cuts out

 

[Darkmagi666]

Ianmcd, I tried as you suggested & the boiler read a constant 48c but as soon as I turned the bath hot tap off it went up again to 67c then the boiler cut out, I did replace the thermostatic cartridge as I had the old one out & the rear of it was damaged but no change at all, When I turn the flow up in the shower the heat stays constant at 62c at the boiler & 45c at the tap but then the water sprays everywhere, I'm thinking I might have to change the showerhead as it's a small pole with about 12 holes in it so I'm thinking the flow is not fast enough & the water is overheating, when my wife has a shower the flow is about 6 litres a minute & it cuts out but if I raise it to 9 litres a minute the boiler stays constant at 62c but if I reduce the temperature of the shower to 34c the boiler cuts out ?

The showerhead looks like the attached pic.

 

[ianmcd]

Yep you have a flow rate problem, try turning the HW temp control on the boiler down to about 3/4 on the dial

 

[Darkmagi666]

Ianmcd, I tried turning the dial down to 3/4 & the boiler cut out at 59c turned down to half way it cuts out at 54c I'm thinking of getting something like the attached pic to hopefully increase the flow rate.

 

[ianmcd]

first remove the existing shower head and run the shower with just the hose attached and see what happens, if it still cuts out you have a restriction somewhere else, if it doeasnt just fitting a decent flow shower head should sort it

 

[Darkmagi666]

I took the showerhead off to get a flow reading & at the flow my wife normally has it the flow was about 6 litres a minute & it still cut out I then turned the flow up to 9 litres a minute still without the head on & the boiler ran at a constant 62c with the temp at the hose 44c

 

[ianmcd]

Then just get a high flow rate shower head

 

[Darkmagi666]

Sounds like a plan, Thanks for all your help

 

[bernardgreen]

Yep you have a flow rate problem,

possibly aggrevated by the temperature of the cold water supply being higher than normal.