I have a Vaillant combi boiler and recently i have been having a problem with the shower. Everything else is ok, the radiators are fine and the hot water when turned on in the downstairs and upstairs sinks runs forever. My son was having a shower yesterday and the hot water light on the boiler would light up for about 30 secs giving hot water, go off for 30 secs giving cold water, light up for 30 secs giving hot water and so on. I thought it must be a build up of scale so i took the shower head off and de-sclaed it for several hours before re-attaching it. However turning the shower on again earlier it behaved in the same manner as before so im not quite sure what the problem is. Any help would be appreciated. Thanks.
Hot water in shower cuts out/cuts in
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Thanks for the tip on having a continuous hot shower. What is the easiest way to check the flow rate.
see if it will put at least two litres into a bucket before your watch counts 120 seconds? 
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It probably will. The only problem is it will be 30 secs of hot water followed by 30 sec of cold water followed by 30 secs of hot water then 30secs of cold water. The actual flow seems constant its just that the hot water comes on and off.
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Plate exchanger blocked or gas valve set up incorrectly. Post back the model of your Vaillant boiler to stop a lot of second guessing When was the boiler last serviced?
When was the boiler last serviced?Well ive been living here for just over a year and the previous owner said the boiler had been serviced 6 months ago. I dont have the manual so where can i find the model.
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Has the boiler got a door covering the controls? If so does it open sideways like a door, or flap down? What colour are the knobs on the fascia?
It does have a door which opens by pulling it towards you and it opens from left to right. The colour of the knobs are green.
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It sounds like an early Turbomax, it will also have a black fascia and a vertical row of LEDs on the left.
This boiler doesn't have any diagnostics like later models, so I can't help you too much more other than saying as before its probably a blocked plate exchanger or the gas valve is misadjusted. If the hot water light next to the tap symbol stays on when showering, but the flame and 'egg timer' (ignition) go out then the water section and diverter valve are OK. It's then a heat transfer problem with the plate being blocked top of the list. Try turning the hot water temp control to 8/9, that should help the cycling. Otherwise get a Gas Safe engineer in who can diagnose problems on Vaillant boilers.
This boiler doesn't have any diagnostics like later models, so I can't help you too much more other than saying as before its probably a blocked plate exchanger or the gas valve is misadjusted. If the hot water light next to the tap symbol stays on when showering, but the flame and 'egg timer' (ignition) go out then the water section and diverter valve are OK. It's then a heat transfer problem with the plate being blocked top of the list. Try turning the hot water temp control to 8/9, that should help the cycling. Otherwise get a Gas Safe engineer in who can diagnose problems on Vaillant boilers.
O.K Ive looked at this again and this is what is happening . Ive turned on the shower upstairs and come downstairs to look at the boiler to see what its doing. What happens is that ALL the lights on each symbol will light up for approx 30 secs and you have hot water and then they will ALL go off like you have never turned the shower on in the first place and the water goes cold. This will continue like this for as long as you are having a shower. Ive found that if i turn the hot tap on in the sink area then all the lights on all the symbols light up AND stays like that for as long as you have a shower. Obviously i cant do this everytime i have a shower as i need to have the problem fixed. Does this help any further to determine what the problem is.
O.K Ive looked at this again and this is what is happening . Ive turned on the shower upstairs and come downstairs to look at the boiler to see what its doing. What happens is that ALL the lights on each symbol will light up for approx 30 secs and you have hot water and then they will ALL go off like you have never turned the shower on in the first place and the water goes cold. This will continue like this for as long as you are having a shower. Ive found that if i turn the hot tap on in the sink area then all the lights on all the symbols light up AND stays like that for as long as you have a shower. Obviously i cant do this everytime i have a shower as i need to have the problem fixed. Does this help any further to determine what the problem is.
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OK from what you have now said its looking like (in order of probability)
1. a very small split in, or a stretched diverter valve diaphragm.
2. a faulty diverter valve microswitch.
3. a damaged governor in the diverter valve bottom section
4. a partially blocked venturi in the diverter valve bottom section
Problems on the diverter valve are difficult to diagnose because the symptoms appear to be very similar till you are actually in front of it, and can eliminate by dismantling and checking. You could double check the shower head is not scaled as well. Most showers only draw 4-7 litres per minute of hot when mixed to a warm showering temperature, that shows up this sort of problem when a hot tap on 9 L/min won't. A scaled shower head just makes it worse
You still need an experienced engineer to correctly diagnose.
1. a very small split in, or a stretched diverter valve diaphragm.
2. a faulty diverter valve microswitch.
3. a damaged governor in the diverter valve bottom section
4. a partially blocked venturi in the diverter valve bottom section
Problems on the diverter valve are difficult to diagnose because the symptoms appear to be very similar till you are actually in front of it, and can eliminate by dismantling and checking. You could double check the shower head is not scaled as well. Most showers only draw 4-7 litres per minute of hot when mixed to a warm showering temperature, that shows up this sort of problem when a hot tap on 9 L/min won't. A scaled shower head just makes it worse
You still need an experienced engineer to correctly diagnose.
Thanks for all your help on this. Final question whats the best way to find a trusted boiler engineer who knows what his doing and wont rip me off.
M
mysteryman
I would check the shower if that is the only outlet giving problems. The mixer may require cleaning and lubricating.
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