Combi Boiler - Intermittent hot water

[Soulassassin]

We have a Glow Worm 30cxi condensing boiler and lately the hot water goes hot then cold for a bit then hot again and so on. As the boiler is in the garage I can't tell if its giving an error code or anything as the water is flowing hot again by the time I get there. Seems to happen more when Im in the shower as running a tap or a bath it doesn't seem to happen so I'm guessing its something to do with the water getting too hot due to less flow and its cutting out (the shower is a thermostatic mixer shower). Ive felt the pipes going into the shower when it happens and its defo cold water from the boiler and not a shower fault.
Anybody got any ideas of what the fault could be and cost of repair?

[B B Leo]

hang fire for a bit mate. could be a flow problem not ur supply but more to do with the leaks all the water companys are having reducing the flow to ur house!!

[marvyboy]

could be a clogged heat exchanger had the exact same problem with mine earlier in the year it's the same model as yours...was fixed under british gas 3 star service plan...

marv.

[Soulassassin]

We do have pretty poor water pressure here, the boiler will only go to 1.7bar but it don't seem any different since the problem started tbh.
I'm hoping its not the heat exchanger (again) we've had this boiler about 5 years, fitted by british gas and just after its first years service it had a problem with the heat exchanger. Turned out to be sludge in the system which the engineer was a bit miffed about as it was an entire heating system that was fitted and no sludge should have built up in that time. We got rid of the home care because we were that pissed off with BG in the end. Looks like we're still paying for the shitty job they done in the first place.
How much would a new heat exchanger cost, fitted?

[plug1]

Iv had this , turned out it was the diversion valve.
Hope that helps.
Plug

[sniper]

can't help with boiler but have a look here http://www.britishgas.co.uk/products...ml#one-off-top max. I pay is £130 inc parts / labour if I have a problem under the priority response , costs £3 / mth and it states that no cover for 1st 7 days but when I rang up they were happy to get me signed up and get an engineer on his way .... I signed up cos I knew part was over £200.

[Soulassassin]

Went in shower today and it happend after about 5 mins, stood back and the water went hot again after about a min. But I noticed when I got out the shower the radiator was quite warm. Its the 1st radiator in the system and the heating was off. So kinda makes me think it might be the diverter valve.
@sniper. Although the b.gas thing might be good and might save me money the shit we've had to put up with them so far its simply not gonna happen. The system was fitted by them in the 1st place. Thanks anyway.

[Soulassassin]

Think I have this sorted now. Only been in shower once since but it worked fine.

It was the 'Diverter Valve Motor' that plugs into the side of the diverter valve. Got one off ebay for £20. Bit finnicky to get the part in and out but easy to fit assuming you dont have a moment of stupidity like I did. Removing one of the clips thats in the way then getting a full on face full of water and about 20 mins trying to force the little bastard back on, guess I'm just lucky it wasn't hot at the time.

[Soulassassin]

Well the piece of shit still done it. Changed a thermostat and it seemed okay but temp still flutuates a bit so dont think its solved. Today it came up with an F5 fault, switching back to the older thermostat stopped that and now the temp just fluctuates (not freezing).
Think Im going to get a new boiler as there seems to be no point throwing money at this time and time again.

[Realist]

I did post up the service manual but due to the forum problems we must of lost a few posts.

Find the manual HERE

Regards

[Soulassassin]

I did post up the service manual but due to the forum problems we must of lost a few posts.

Find the manual HERE

Regards

I do have the manual thanks. The link is to a different one tho (maybe older/newer)
Ours is
G.C. No. 47-047-24

That one is

G.C. No. 47-019-02

[Realist]

My manual is from 2006 I think.

[Soulassassin]

Stuck the shower on and went into garage to see what happens when it goes cold.
The boiler trips out with a F5 fault, before resetting itself.
The manual says.. F5 = Overheat Fault.
I'm guessing this is as earlier stated the heat exchanger. I refuse to pay for another one as this would be the third in 5yrs and I see no point throwing money at this anymore. Gonna see how long I can bare it till I give up the ghost and buy a new Worchester or Vaillant.