Heating pressure increase when tap is on

[djembecaz]

Sorry, I'm a newbie but just wondered if anyone had some thoughts on this.

My Vaillant Ecotec 831 boiler was installed a year ago. In the summer it needed topping up once or twice and over winter when the heating was on it was falling from 1.1 to 0.4 bar over the space of a month.

Three weeks ago the heating engineers fixed a small connection on the radiator and added sealant to the system.

Now the pressure remains around 0.9 - 1.5 bar but when it's been off for a while it falls to 0.7 and starts flashing.

If I then put the hot tap on the central heating pressure rises back to 1.1 immediately.

Any ideas on why the pressure would fall when it's off and why turning the tap on might fix it? Something to do with the diverter valve??

Thanks everyone!

 

[Tipper]

It's called thermal expansion.

Water in a confined space, i.e. your boiler and heating system, will expand when heated and contract as it cools. That is all you're seeing.

I suggest you top up the system pressure a bit so that when it's cold it doesn't get so low as eventually it will lock out on low pressure and you will have no hot water!

 

[ianmcd]

Its the effect of your pump running when you open a hot tap, top the standing pressure to between 1 and 1.5 Bar when the system is cold

 

[djembecaz]

Thanks to both of you! It sounds like it's not a big problem then. I'll top up the system when it's cold and keep monitoring for a while to make sure that the engineer's fix has definately worked.

Many thanks indeed!