Boiler firing up when cold water drawn

[willougs]

Hi all

Would be grateful of some advice. We have a Worcester Bosch Greenstar boiler in our utility room, which is fed from a cold water pipe that also tees off to a nearby outside tap and cold-water only machine machine.

Recently, I've noticed that when the tap or washing machine are used, the boiler seems to do strange things.

• With the outside tap, as soon as I shut it off, the boiler kicks in (with the hot water tap symbol) for about 2 seconds, as if I've just turned on a hot tap somewhere in the house.
• With the washing machine, each time it takes on cold water, the boiler seems to go through a cycle of pressure gauge dropping, it whirs for a bit and stops, at which point the pressure goes back up. As the washing machine seems to take on water often during a cycle, it does this every time, sometimes just a few seconds apart.

I've not noticed this behavior until after we recently had the boilers plastic filler key and value replaced (as water poured out once key was removed) and I've therefore been keeping an eye on it. I cant say for sure though that it wasnt doing it before.

We've also recently had a new bathroom fitted but everything else appears to be in order. Hot water comes out of hot taps, cold out of cold etc. It also only seems to be the 'appliances' right close to the boiler that cause this. (i.e. opening cold tap in kitchen doesnt cause boiler to think there's a demand for hot)

Can anyone please explain what the boiler may be doing? Whether it's to be expected? And whether there's anything to resolve?

Thanks in advance,
Steve

 

[DP]

If it is a recent fit, get the installer back. You have trapped air in a pipe that is capped when the boiler was fitted.

 

[DaleRCL]

DP is right. There is air trapped in a dead leg of one of your hot pipes where the installer has capped it instead of cutting it back as he should have. When you run the cold, the pressure in the hot pipe is dropping allowing the air to push back down the pipe and when you turn the cold off it charges the dad leg back up giving your boiler the illusion that hot water is being drawn off, hence firing the boiler. Get him back and ask him to completely remove all dead legs.

 

[ianmcd]

Good luck with that , yes I agree it is a dead leg , but doubt if your installer will sort it FOC

 

[DaleRCL]

I didn't say he should do it free of charge