SIMADDOX - Worcester boiler pressure problems.

Simaddox's enquiry:

Last April we had a new Worcester Ri high efficiency gas heat only boiler fitted by a WB approved installer (who has been brilliant and who we cannot fault). As the boiler is in the loft, there is not enough head pressure to run on a gravity basis, so the entire heating system is pressurised but only to the existing head pressure. This has been done via a 15 litre expansion vessel and guage sited in the airing cupboard.

The installation was completed on the 14th March 2014 and by the 22nd I had noticed that the pressure was fluctuating between 2bar (when running) and 0.7bar (when cold). Then on the 28th March the cold pressure dropped to 0.3bar and the boiler failed to fire. I replenished the water pressure by opening the inlet tap for just a few seconds. The pressure went up and the boiler fired.

This cycle was repeated at an interval of (on average) 22 days until I turned the heating off at the beginning of June.

When the heating system was restarted in September with a reduced boiler temperature, it was fine for nearly two months, then when the temperature was turned up for the colder weather, the cycle resumed. It is now running on an exact 16 days cycle. The hot pressure stays absolutely static at 2 bar and the cold pressure stands at 1.5 bar for a fortnight - then the cold pressure goes right down and the boiler fails to fire. Now I know it will happen after 15 days, I am tempted to refresh the pressure on the evening of the 15th day rather than wake to a cold house in the morning.

The Engineers who fitted the system have been brilliant. They have been out numerous times and have checked everything and have fitted a larger expansion tank. However the problem continues. They felt that there must be a leak in the radiator system somewhere so filled it with a leak sealant. As there is no visible sign of a leak, they now want to look under the downstairs floors. However, we are reluctant to do this as we've just had new carpets, wooden floor and Amtico covering in the kitchen.

Any ideas?

 

Nope.

The only thing I was going to suggest was a larger exp vessel, but they've done that. The reason I was going to suggest this is because a running pressure of 2 bar is really too high, and is not too far from possibly opening the safety release valve. Certainly uncomfortably high, so that's something I'd like sorted regardless of anything else.

Since they fitted the larger exp vessel, has there been any improvement in the 'hot' pressure - ie has it become a bit lower, or is it still 2 bar?

Anyhoo, one thing I'd like to determine - is there any water being lost out the safety discharge pipe? That should help to identify the cause of the lost pressure.

Wrap a small clear poly bag around the pipe outlet using a rubber band or similar, and keep an eye on it.

That fact that the pressure drops suddenly after a certain time doesn't necessarily mean that's when the pressure is being lost. Ie, it's not necessarily fine, fine, fine, fine, oops - lost water.

It could be that the exp vessel is doing its job - maintaining the pressure even when system water is being lost slowly; ie the vessel compensates for the gradual loss of system water, until it can no longer do so.

Of course, it could also be that it's all fine for a goodly time, and then the hot pressure goes a wee bit higher than usual and then it does dump the system water in one fell swoop out the discharge pipe.

That's why you need to monitor this pipe each day until the system next needs topping up. It should be a good pointer as to what's going on.

 

That discharge pipe should be outside, not up in the loft...

 

Blimey - what is it discharging on to - the gutter? A hopper? People's heads... ?

 

That is sooooooo wrong. And I'm pretty sure breaks regs.

When that PRV opens, your are getting near-boiling water being ejected at over 3 bar pressure. Not a shower I'd like to be under...

 

Sorry, nope...