Potterton Performa - Shower cycling between hot and cold

First post so please go gentle on me.

I have been thinking of asking gurus here what could be causing my Potterton Performa to cycle between hot and cold shower. I mean it starts cold and when we let the water run for a while in a minute or so it gets warm and then again goes cold, this cycle continues.

I did some diagnosis myself and found out that the pin which sticks out to turn on the microswitch when hot tap runs doesn't come out if we open tap a bit, it only starts coming out when we fully open the tap and by then water starts splashing due to excessive pressure. Pin is hesitant to come out for some reason. I thought this could usual diaphragm and replaced it myself, old diaphragm was in good condition and it didn't help at all, problem still continues.

As this problem has been going on for a while we have found a workaround, which is to turn the heating on. When we turn the heating on, other pin easily comes out and turns the switch on with no hesitation. This is kind of workaround we have been living with for a while now. I wish I can get to bottom of this. Can someone please advise what could be wrong here and if there is easy fix.

 

Sounds like you got a couple of faults, the on/off is probably being caused by a blocked plate heat exchanger and the high flow needed to start hot water by a faulty venturi.

 

the easy fix would be a repair engineer

 

definite faulty venturi . do a search on here for venturi on baxi 105 .
its the same boiler

 

All the engineer they have looked at it say I need new boiler which I am bit reluctant to. This must be fixable but none of the engineer wants to touch it for some reason. I find this behavior bit weird! It must be fixable instead of me spending £2k for a new boiler.

We don't have problem in winter as heating is pretty much on most of the time so hot water comes as it should.

Is it easy to replace venturi?

 

Yes its an easy repair, whereabouts in the country are you ? there maybe someone on here that could fix it for you.

 

Ruislip, London.

 

From walking into house to walking out should be less than 30 mins for this repair and part is about 14 quid, an hour max if someone wants to do a few other bits

 

....plus collecting said part...mark up on said part......travel time to fit said part.......has Agile cloned your log in details..

 

i said how long the actual job would take .The other stuff is all down to location of repairer and job address .
I would pick part up on way to job and be at job in less than 15 mins . PC is 5 mins from house and i dont have to work more than 10 mins from house . The joys of picking and choosing work
oh i imagine the mark up on top of a 14 quid part must be in the 1000`s of % .

 

So you are 100% sure it's the Venturi??...and happy not to attend in order to diagnose?...

 

Which bit of problem faulty venturi is responsible for? Pin not sticking out as it should or hot and cold cycling? Part of problem is pin not sticking out if I open tap slightly, it comes out when tap is opened up fully and then also it will do cold and hot cycle.

how do I fix blocked heat exchange plate?

 

sorry got it, venturi will solve pin not sticking out problem. But how to fix blocked heat exchanger plate?

 

just get venturi sorted first which may sort your problem but it all depends on the info you provide