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brooklyn07

Hi All, I would really appreciate some help/advise with aboiler problem I am having.

I have a valiant eco tec combi boiler and have noticed thatwhenever I flush the toilet downstairs, as soon as its finished filling theboiler kicks in…. the orange light turnson and I can hear the flame ignite and then goes off again a few seconds later.

The same thing happens when I turn off the cold water taps in the rest of thehouse.
I have recently had the upstairs sink and toilet swappedaround and my dad (was a plumber in the 80s) connected the sink up for me usingthe existing copper pipes and grey plastic (hep20?) pipe.
He created a T from the cold water with the plastic pipe tothe toilet but this is not yet connected its just sitting there at the momentwith a plastic cap over it ready for next weekend.
I cant be sure if the upstairs bathroom reconfiguration hascaused this because the boiler was switched off for 7 months whilst renovationwork was being done (nothing that involved pipes or anything just electricaland knocking down a wall) so I cant say Ihave noticed this problem before and whenever I have used the downstairs toiletI have immediately gone to the hot water tap before the loo has had chance tofinish filling so any boiler operation wouldn’t have been out of the ordinary.
I had the boiler serviced about 2 months ago and all wasfine although the cold taps and toilet were never operated so again problem wasn’tnoticed.
When the sink was fitted upstairsmy dad asked me to turn the stopcock off downstairs and then switch some tapson to make sure it was definitely off. The stopcock was turned on and off twiceduring the course of him fitting the sink (incase that has any relevance)
I cant get a plumber out just yetas I cant have any time off work for another 2 weeks so im hoping I might beable to sort it before then,
Did some googling and a lot ofthe answers seemed to push towards a dead leg in the system. The only place I haven’t looked is under thefloor but I have looked in obvious places such as old airing cupboard and inthe attic and haven’t found anything.
Only “dead legs” I have are thehot and cold feed for the washing machine as I don’t have a washing machineconnected just yet (and when I do will be cold feed only) they have the red andblue valve things on the end of them, and of course the pipe to the toiletwhich is yet to be connected.
So I then thought perhaps thereis some air in the system so followed some instructions to turn off stop cockturn on all taps and tried bleeding the hot and cold washing machine feed.
Turned on the stopcock and thenran the hot and cold taps for a few mins each including the hot and coldwashing machine pipes but still the problem persists.
Another thing ive noticed whichim not sure is relevant but the taps upstairs in the bathroom seem to have highpressure so I tried turning the stopcock down and since then I just get a “pshhhhhhhhhhhh” sound for a few secondsafter the taps are turned off so I turned it back up and the noise stopped….
Any ideas what else I could tryplease??



 
Have you got a non-return valve on the inlet of the domestic cold water supply to the combi boiler?
 
I'm not sure to be honest would it be in an obvious place? would it be on the same pipe as where the filling loop is? I remembered there are some isolation valves on there somewhere but I don't even know what a non return valve looks like so I'm off to google that....
 
Are the basin taps right ie hot on left cold on right, were they that way before the basin was changed or was the cold on the left...
 
yes on the old sink the hot tap was on the left and on the new sink I have to turn the mixer tap to the left to get hot water.
 
He created a T from the cold water with the plastic pipe to the toilet but this is not yet connected.
This might be the problem as this pipework might be full of air initiating your boiler to call for heat.
 
high water pressure is the cause, turning off a tap or cistern filling stops causes a shunt in the cold pipe work and the flow valve in the boiler picks up on this causing it to kick in. get a technician to install a prv on the cold main for starters and a shock arrestor on the boiler cold feed and the problem should go away
 
high water pressure is the cause, turning off a tap or cistern filling stops causes a shunt in the cold pipe work and the flow valve in the boiler picks up on this causing it to kick in. get a technician to install a prv on the cold main for starters and a shock arrestor on the boiler cold feed and the problem should go away

boilers with paddle flow switches seem to suffer most from this issue in my experience.
 
I have seen a bank of toilets in a hospital that were crossed in just that state ..was quite a spectacle haha
 
Common problem, fitting a mini expansion vessel on the cold before the boiler should sort it.
 
You can delay the flow switch in an ecotec, might cure the surge from kicking the boiler in...
 
Thanks forall your replies everyone.. The upstairs toilet was plumbed in yesterday and it didn't make the problem to away unfortunately.How would I delay the flow switch is this something I should be messing with or do I need to give up and call someone in...
 
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