Baffled by my boiler! Please help!

[transam]

As far as I am aware , the boiler has a flow switch on the mains supply that requires a min of 2.5 litrea a min to fire boiler , in the h w mode the boiler will fire on max gas rate & than modulate down on temp / flowrate , in c.h mode the boiler will light on ign pressure , than modulate to the heating load , providing the stat is not at max , we fitted a couple years ago & I have a few dog eared hand written notes , which may ? be accurate ????

 

[bcoleman]

Morning All - Thanks for all your help so far.

I've just tried a few things and think I've found the cause of this problem -this is what I did:

1. turned hot tap on on it's own = nice hot water and the temperature doesn't seem to fluctuate (always too hot to put my hand under)
2. left hot tap on and added some cold = after a bit of playing around, a nice warm temp
3. left hot tap on but turned off cold = goes very hot for a few seconds, then cold, and then hot again

I think this means the boiler is modulating down when the cold is added (as the flow is lower through the boiler, right?) and then when you turn the cold off, it modulates up again but there is a slght lag (ie. burst of cold water through the hot tap) before the temp gets back up again.

Does this make sense? If so, I'm assuming the problems I'm having whilst showering under my manual mixer is that the cold flow/pressure is fluctuating as other people down the street are using it- thus causing the boiler to modulate as it should but it doesn't modulate quickly enough and the temperature under the shower therefore fluctuates up and down?

If this is right what options do I have? I've tried playing with the DHW knob on the boiler with limited success but would a set of termostatic mixer taps work or am I stuck with this for good??!!

Thanks for all the help so far and any further info would be brill!
Ben

 

[Agile]

My experience of these situations is that the mains pressure into a property does not have short term pressure variations over say 10 minutes.

Are you sure no one else in the house is using water? That includes washing machines and flushing toilets and cold in the kitchen.

I am not a fan of thermostatic showers as I get so many calls about problems with them.

My advice is always to take a good flow of hot water to the shower and turn DOWN the boiler DHW temperature until its about right to shower in and then add just a VERY tiny amount of cold water to make the final adjustment downwards in temperature.

Most of the problems usually found are caused INSIDE the property by high resistance water supplies which alter the pressure when the flow is altered such as toilets being flushed.

A simple way to monitor flow rate and hence pressure without equipment is to run a kitchen mixer tap into an empty flat stainless sink and see how wide the circle formed by the water hitting the bottom of the sink. Thats quite a sensitive indicator of the flow rate and watching it as other water appliances are turned on or off will show how much the flow is being affected.

Tony