The last couple of mornings when I have had showers the hot water coming through the shower has been cycling from almost too hot to almost too cold over about the period of 2 minutes. The outside airtemp has been considerably cooler than late, as is the cold water temperature coming in through the mains.

Both the combi boiler and Triton Mixer shower are both just under a year old, so not happy if either are starting to go faulty already.

So is it likely to be the mixer valve in the shower, or the boiler not regulating the water flow? Hot water from a tap appears to be coming out at a constant temperature, but then again I don’t leave it runnung as long as the shower. Mrd FD ran a bath last night and she said she struggled to get it warm enough though. We already have the water temp thermostat sat just under max on the boiler as it is…

Any ideas.

Ta

If it’s a combi boiler the favourite will be the heat exchanger plate, fairly easy to fix, on mine the symptons were hot water on, heated up, boiler turned off, cold water, boiler on, hot water, the effects were worse the further from the boiler the taps were, caused by crud gathering in the exchanger giving a false output for the boiler (restricted water flow boiler thinks the water is still hot but its not). When replacing the heat exchanger they are usually sealed with rubber/neoprene washers ensure that these are changed for new ones. Fairly easy change over no need for a boiler stripdown in most cases.

yup, sounds like boiler, could be plate heat exchanger, thermistor, pcb, water filter. take your pick!

Servicing the boiler would be my first task, as you probably should do it after the first year, and every year, anyway. When I did mine after 18 months there was a build up of cack on the heat exchanger and I am sure it ran a fair bit better once it was done.
Check pressure of water into boiler is ok.
Could be the shower thermostatic valve but if it’s poor running the bath this may not be the case. Remember as it’s winter the water is colder going into the boiler so it will struggle to heat it to the same temperature, if you don’t turn the tap on to max the water will stay longer in the boiler and heat up more. Does seem an odd problem though.

So if the boiler is under a 5 year manufacturer gurantee we need to get them out then?

Yes, what boiler is it? Was it power flushed or at least he sludge remover added for a week before installation?

your shower needs 60-65degt hot water at 8lts water flow, your boiler is not holdind this and is cutting out. could be you have hot water turned to low on controls poor flow but more likly you need to get it seviced and check water flow and hot water temp stat. easy way to check if boiler or shower hold onto hot pipework to shower if this goes cold its the boiler if it stays hot put shower going cold possible its the shower .if your shower needs flow limiters fitting check instruction book have they been fitted?

It’s a Viessmann vitodens 100 – 35kw with an external temp sensor.

The system was all brand new last xmas. The fitter got it up and running as major building work wa going on then he came back 3 or so weeks later and put some kind If additive in the system. He said that any problems whilst under gurantee we would need to deal with viessmann direct…

He said that any problems whilst under gurantee we would need to deal with viessmann direct…

Well that isn’t correct really is it? Your guarantee is with the supplier not the manufacturer. I would ring him up.

(EDIT: This is the case for the first period (usually 1 year) – in the event of an extended warranty claim, it might be correct to contact the manufacturer).

Yep definately manufacturer its a 5 year warranty thing, just spoke to them and they are hopefully coming out tomorrow!

The boiler was fixed yesterday.

Turns out that the fitter hadn’t fully opened the cold water inlet valve properly so not enough cold water was getting through the boiler which was making it over heat and therefore make the boiler automatically cool down in a cycle. Now hot water is overall hotter, and the shower runs at a much higher pressure.