Worcester Bosch 30I Combi boiler pressure

paulcam

Hi,

So this isn't a post about a fault with the boiler. It's brand new, literally less than a week old and functioning fine.

As it's a new boiler installed into an older heating system I expected some pressure loss and will keep an eye on it. After the first 4 days or so I checked it, to find it had fallen a little, gauge red just 1 bar. I pulled the blue filler valve and heard water enter slowly. After about 30 seconds the pressure was up to about 1.3bar, well in the green.

Checking it a few days later and it had fallen very slightly to about 1.2bar, so I pulled the fill valve again. Nothing. No inflow, no noise, no pressure increase.

So either that fill valve has other checks in place, such as the boiler has to be cold and completely off or... my mains pressure is insufficient at the moment to add more pressure.

I assume I am fine running it at 1 bar as the green area on the pressure gauge extends just below this. However I believe the optimal cold pressure is 1.5 bar. If my mains water cannot provide 1.5 bar, how worried should I be? Can I do anything about that? Should I ask the local council/water board what pressure they guarantee?

As an aside the only other slight annoyance I have found that might be particular to this boiler... if you open a hot tap while the heating is running the boiler shuts off. It then restarts 20-30 seconds later. So the total delay time on hot water can be as much as a minute. Previous Combi boilers I have lived (Baxi's) with have been capable of switching direct from heating to hot water without a restart, though would enforce a restart going the other way.

Talldave

When the flat I was renting had to have a new boiler, we went from non-combi to combi. The gas bill went down, the water bill rocketed. Overall, total bills went up, as did my blood pressure waiting for hot water to appear. The full shutdown before supplying the hot water demand doesn't sound right though - might be worth asking Worcester?


The house I'm renting now has a beautiful 300 litre hot tank that is superbly insulated and takes only a few minutes a day to heat up. I'd never fit a combi if I owned a property.


Back to your issue though - are there two valves on the fill loop? As the system's only recently been drained, it would be worth bleeding all the radiators and then topping up the pressure. If it's keeps losing pressure long term that does point to a leak.

matelodave

It can take a week or two to settle down if the system has been refilled recently as the dissolved air in the system gets dissipated.

I dont know about your boiler but some do have an automatic bleed valve (ABV) which should allow air to escape and will therefore allow the pressure to drop.

As said, make sure your rads are bled - generally the pressure sits at around 1-1.5bar, so anywhere within the green zone is OK.

My heating system was topped up to 1.5 bar around two years ago and has gradually dropped to just over 1 bar since then so it's probably about ready for another top up.

We did have a fairly rapid (over a couple of weeks) pressure drop about 4 years ago which was due to a gunged up ABV, easily replaced.

paulcam

Yea. I'll bleed the radiators and top it up. Slightly worried that the fill valve isn't working anymore, so I'll bleed one radiator and check it will fill again. Mine has just a single little blue tab you pull down underneath to fill. It feels like an actual valve being pulled open, but maybe it's not.

On the hot water cut out, I think I figured out what is happening, having done some tests.

I was using the bathroom shower, which is run off the bathroom taps as I haven't got to the point of replacing the now defunct electric shower with a mixer shower.

When I pull the tap up with it set to where I left it last time it opens both hot and cold taps, but as it's a mixer tap it then restricts the hot water flow enough to cause the boiler to cut off. If I open the tap in full hot this doesn't happen. If I open it at the mid point the boiler comes on, then cuts off and the hot water symbol disappears. I need to open it set to HOT only and then move it across to where I want it quite slowly. As soon as it starts to restrict the hot flow the boiler cuts out.

I'll ask Worcester if that flow rate is adjustable to make it less sensative, but I expect not and, in real world showers it hasn't been a problem and when it's on it stays on, it just gets upset when starting the hot water through the mixer tap is all.

paulcam

Worcester support confirmed that the boiler will activate with a very low flow rate on the hot tap, but if the flow is restricted to where the boiler can't back off enough or quick enough it will cut out.

So I'll just open the tap in the hot position and then feed in the cold slowly and try not to overshoot the normal shower temp.

Thinking about it, my previous combi in my last place the mixer shower I would always open fully to fully hot and allow the water to warm up, then bring it back towards the cold to find where I was comfortable to get into the shower. Just same thing here then.