Hello. I've just moved into a new house. The water from the kitchen tap takes ages to heat up and doesn't get properly hot even though I have turned up the water temperature on the boiler. The water in the shower doesn't run cold even if I turn the dial as far back as I can towards the cold setting. I have a combi boiler. Is this a boiler or a plumbing issue?
Combi boilers do take some time to provide hot water. Most of them now have a facility to provide almost instant hot water. This is achieved by means of a small tank within the boiler which is kept hot and provides the first slug of water before the boiler has a chance to catch up. The downside to this is that the boiler is continually firing up t keep this tank heated and, especially with gas prices as they are, this is expensive. For that reason most combi boilers have the facility to turn this pre-heating function off. Doing so means you will have to wait for the boiler to bring the water up to temperature. Check on your boiler to see if this is the case. The control is often marked "eco" or "pre-heat" or something like that.
NewJudge could well be right about the tap issue.
You may need to select the "pre-heat" function. (Not the "Eco". That's something completely different.)
With the shower, I would normally suggest a faulty shower cartridge.
I guess you mean it's a house that's "new" to you, as opposed to a new build?
With new-builds, the most common cause is debris in the pipework, which can quickly bung up a cartridge valve.
//(Not the "Eco". That's something completely different.)//
Mine (Worcester) is exactly that, builder. Enabling the "eco" facility simply disables the pre-heat system. It's sold as being "eco-friendly" because it does not continually re-heat the water as soon as it cools. Of course "Eco" may have a different meaning on other makes/models.