Worcester Bosch 37CDi - losing pressure / needing refilled

I had a 37CDi installed in October last year and it's worked well until last week. We awoke in the morning to find the DHW not coming through the taps and it turned out the boiler pressure had dropped to zero. I refilled the boiler up to 1 bar and everything was OK.

Since then, it has dropped very slightly every day (about quarter to half a bar every couple of days). I have made a couple of assumptions which may be totally wrong but:

1. As the CH is not being used at this time of year, it is unlikely to be a leak in the CH pipework as no water is flowing in this system
2. As the pressure drops overnight when no DHW is being used, as well as during the day, it is likely to be a boiler issue.

As I say, these are probably wide of the mark and don't help diagnose the fault anyway.

The boiler is under guarantee but I'd like some info to go to them with if it is the boiler and I'd like to avoid a call out fee to a heating engineer if it is likely to be a fault that is fixable under guarantee.

Any ideas of what the problem might be?

Water can leak from the ch system all the time. It doesn't need to be being used for it to leak and lose pressure.

Have you checked the prv discharge pipe out side from the boiler for dripping etc?

If ok, pressurise boiler to normal, isolate ch system with the valves under the boiler, leave as long as possible, then open the valves.

If pressure drops whilst ch is isolated then leak will be on the boiler. If pressure drops when isolating valves are re-opened, then leak is on heating system/rads.

Though g4u has given essentially correct advice, due to the boiler being less than a year old, I would recommend against any diy and get the installer to have a look at it. There is always a chance that you do something wrong and cause damage somehow, and any half decent installer will have no problem with a quick check.

Thanks to both of you - I'm happy to isolate the CH (I assume it's only turning a the screw half a turn to close off the fitting, same as a standard fitting at the WC or other isolator etc...) as no-one will be able to detect whether this has been done or not.

At least then I'll know if it's the CH or boiler.

If it's the CH the boiler installer is unlikely to be too interested, as the boiler was fitted as part of an extension to the house, though he did add three rad's...

Am I right in thinking the CH flow and return are the 22mm pipes at the outside of the boiler connections - it looks this way from the manual but best to check.

Thanks again

Yes ch will be 22mm pipes.

Shutting these isolating valves won't have any effect on the boiler warranty.

Have you noticed any damp patches on the floor or ceiling, or any slight drips around the rad valves?

Haven't noticed anything at all in terms of damp patches or drips, but it's only losing a small amount (I think). When the problem first presented itself last Tuesday, the small square fitting used to refill the boiler, once the filling key is inserted and unlocked, had a slight drip, so I thought that was the likely cause. I've made sure this is tight after topping up each time though, so I don't think that's the root cause.

How long should I keep the CH isolated for once the valves are closed?

Hold that thought - I've just told my wife I have to isolate the heating, I hadn't said anything to her about it before because she would worry about it...

Anyway, she's told me about a drip from the downstairs WC radiator which she dries up pretty much every day (I was blissfully unaware). Nothing too much but there's definitely a drip coming from the fitting at the CH pipe side of one of the valves - this had a TRV fitted when we had our extension built so the fitting is new at that point.

Is a drip like this enough to cause this much of a pressure drop - it would be a relief if this was the problem as no floors would need to come up.....

I've isolated the CH at the boiler anyway to see how it goes.

Just a thought - is the drip likely to be less with the CH isolated, as the system is not under pressure, or is this just nonsense thinking on my part? Just keen to keep an eye on both the boiler and the drip over the next day or so

Any drip is probably worse than you really think.

Fix the drip and see how you get on, then post back