1) My Vaillant says the range is 0>3 bar. So what should I be aiming for when the water/rads is hot? 1.5 or 3.0?

2) How much increase is normal from cold to hot?

Boiler is upstairs in a 2 level terrace if that makes any difference.

Read the manual – not much joy.

Much thanks.

The manual will tell you where to set it when cold,it will rise as it heats,how much is determined by the volume of water in the system vs the size of expansion vessel.Why do you ask?

Normally around 1bar when cold, you don’t want it near 3bar as the pressure relief valve will start dumping pressure, then it’ll start leaking and you’ll be forever topping it up..

Usually ‘about’ 1/2 bar per floor when cold.

So if I were constantly topping up our system, it is probably (possibly) an overworked relief valve?

Another little thing to look for.. M

More likely a leak or an under pressured expansion vessel.

Tie a bag over the prv outlet to check if its the prv or expansion vessel.

1.0-1.5 when cold. Is there a red line on the gauge about that? As it’s upstairs 1.0 should be enough (equates to roughly 10m head, that’s plenty).

0.25-0.5 increase when hot is not unusual.

More likely a leak or an under pressured expansion vessel.

Just refilled our expansion vessel with air – looks like all our problems with the boiler needing topping up, especially when the radiators had all been recently bled, may be solved! Pressure is varying so much less between hot and cold now.

When the boiler was installed 2 years ago it was reading 3bar hot. Thats how the plumber had set it. I never really questioned it too much as no experience with a combi boiler before and for some reason it made sense to me i.e. lots of pressure easier to push the water around the house…

Heating has been on the last few nights and it takes forever to get the rads warm. If I opened them up downstairs the upstairs ones would never get warm even after a hour.

Time to read the manual again – will bleed it down to 1 bar if its right – much thanks stw.

Hi Earl..
If the pressure is between 1&1.5 bar and you still have the issue of slow warm up then I’d be tempted to call a heating engineer mate.. Unless the system has a lot of air in it , which bleeding should get rid of, you might have another problem.

Thanks – cardio – set at 1bar now and going to test it tonight.