The title explains the main issue, for some reason the hot water drops often every 20 secs or so, sometimes it doesn't recognise that the hot is even running right away but always seems to click in within 45 secs?
The shower runs direct from the boiler also and I have to get a 30 sec to a min shower then turn it off and wait 30 secs turn back on and hope I may get another 30-60 secs.
I believe there is loose wire somewhere as shutting the flap on the front anything more than softly sees the boiler power down before firing back up again but I believe this isn't the issue.
I don't know much at all about the workings of a boiler but we did change a pressure valve a while back, I forget what the part is called but we had to remove the casing and then open the boiler up, the valve sits on top of the upright pipe on the right of the boiler and was a pain to fit as even with two wrenches on it there was a third section that wanted to turn lose.
It seems to me that the problem is with a sensor that either tells the boiler when the hot is running but more likely a thermostat which maybe telling the boiler it needs to shut off every time it gets to temp?
The final point of note is that the boiler hs always lost pressure but in 5 years there has been no sign of a leak, the funny thing is that it used to lose pressure every 5 days to 2 weeks but after 3 years it stabilised and seemed much better but lately its losing pressure to a similar degree as before, I wondered about the valve we fitted which was over a year ago but there is no sign of any leak.
The central heating seems fine.
The only thing that has always bothered me is why did the plumbers who fit it leave the flexi pipe in place, they told me if i ever need to add pressure I just need to turn the two handles but I have since been told that the pipe should not have been left although with the average rate that the boiler loses pressure i'd be lost without it! the pipe actually leaks a fair bit of water from the top handle when turned which it never used to do.
Any advice/suggestions are greatly appreciated

Granty, March 2014

It could be a build up of sludge in the heat exchanger allowing it to overheat slightly which would give it a rythmic on/off,when central heating is on it is a lower gas jet so the flow of water is managing to take the heat away from overheat sensor,only a boiler repairer could ascertain exactly whats going on.I would get someone who knows about combi's rather just a plumber as in my experience some people will give you some guff and say it needs a new boiler rather than test it

toptrish, March 2014

Hi, Thanks for your help!
It has never been serviced, I didn't realise it needed to be tbh.
The prolem is with any hot tap and the shower, for exam,ple if either are running the boiler kicks in as normal but then shuts down and then after a while kicks in again and shuts down, it seems to vary a little how long it stays on but i'd say its between 30-60 secs, when it goes off it can take the same to come back on.

Granty, March 2014

There should be an expansion vessel either built into the boiler or as a separate tank,the pressure needs to be checked when there is no pressure in the central heating using a car pressure gauge.have you had it serviced lately? the problem could be a sensor like you say,but I would make sure the pilot light is not being deflected away from the thermocouple when on full power as sometimes happens,I had an oven that did the same thing and the so called experts changed every thing but still did not cure it until i noticed what was happening.Is it only when shower is on or any hot tap?please let me know before i can point you in the right direction

toptrish, March 2014