Shower goes cold if I run hot water from kitchen faucet

[relammers]

hi all, I’m trying to troubleshoot an issue with my boiler. If one person is in the shower at a normal hot temperature and another person runs the kitchen faucet at the hottest temperature then the shower will go cold. Any idea why? I have checked the temperature and pressure on my boiler and all seems to be in fine working order. I’m trying to figure out if I should call out an engineer to look at the boiler or if I can save money troubleshooting this myself. It’s a 5 year old boiler and we haven’t had issues before. Any idea if this is a problem or is this normal?

 

[MACPLUMB]

Simple then DON'T turn on the kitchen faucet when some one's in the shower

 

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[Reach4]

It’s a 5 year old boiler and we haven’t had issues before. Any idea if this is a problem or is this normal?

If it did not happen for 5 years, I would think it is not normal.

Start simply by making sure there is not a partially-closed valve for the water feeding the water heat exchanger. I am not knowledgable in these systems, but a partially closed cold water feed valve seems like it could cause a symptom like this.

If you could temporarily put a pressure gauge on the hot faucet that normally feeds your washing machine, see if there is a significant pressure drop on the hot line when much hot water is being used.

 

[DewPoint]

I’m guessing it was always this way but perhaps you never knew it because no one ever ran them at the same time. If you turn off the kitchen faucet I’m assuming that the hot would return to the shower, yes?