Pressure increasing on a Worcester combi boiler.

16 Apr 2008
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United Kingdom
I have a 9 month old Worcester boiler. The pressure gauge used to read 1 bar cold and 1.5 bar when the heating was on. I have noticed recently that the pressure is slowly increasing and now reads 1.5 bar cold and 2 bar with the heat on. The filling loop is disconnected so what is causing the pressure to creep up? :?:
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had a few of the new ones with internal holes on heat engine. call worcester and have them replace this under warranty.
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Sorry it's a Worcester Greenstar 42CDi. It's still well within limits so I am not panicking but how would this cause water pressure to increase
its corrosion between the dhw and chw waterways. the dhw is allowing mains pressure into the heating side. i hope your installer put flushed and 'INHIBITED' your system. hint hint. :D ;)
could just be gas caused by corrosion; have you bled ALL the rads?
Yep I bled the rads at the weekend and some air did come out of three of them which did drop the pressure a fraction. At separate times I have had to bleed three radiators in the past months as the tops went cold but I put this down to the fact that it was existing air trapped in the system as the system was only filled in May and the fact that I was nosy and have checked the magnaclean a couple of times which might have introduced air to the system.

With reference to the air in the radiators I did wonder if the inhibitor was under strength as I have a total of 12 radiators so a placed a nail on the magnet of the magnaclean and left it a few weeks. The nail came out completely rust free while another nail placed in a bottle containing tap water went rusty. So in total including introducing a nail and removing it I have been inside the magnaclean 4 times so could this account for the air in the rads? Playing on the safe side I did add another litre if inhibitor around 6 weeks ago.

Do people here still think it is corrosion on a 9 month boiler or maybe a manufacturing defect in the water to water heat exchanger?

Question is the water to water heat exchanger just another name for the Direct Hot Water Heat exchanger. I have also read on another thread that it might be a pin hole in this device.
as long as you keep getting air out of the system, my guess would be that the problem lies there.
bleed the lot every day for a few days and see if that keeps the pressure down.
Just checked the upstairs rads and removed more air from the same 3 radiators that I found air in last weekend.

By taking the air out the pressure gauge only drops a fraction and is still around half a bar higher than it was around a month ago.

I have plenty of inhibitor so what is causing the air and why is the pressure gauge still reading half a bar higher than it was even with the air removed?
system warmer than last month when you looked?
as long as the pressure stays between 1 and 2.5, there is not much of a problem in the short run.
if you call and there is no fault, they could charge you for it, so i would wait until no air at all comes out.
you could of course add a litre of inhibitor, only costs about 15 quid
OK I will keep an eye on things. As I have already stated I have a total of 2 litres of inhibitor in my 12 rad system.

Out of interest I check the gauge first thing in the morning before the heating has come on and after a couple of hours after the heating has come on.
what is the difference in pressure between fully hot and fully cold?
just out of interest, don't you have the time set to warm the house up before you get up?
Half a bar difference between fully cold and fully hot.

I get up at 5:30 which is one hour before the heat come on and one and a half hours before the rest of the family gets up. The heating does kick in in the night if the house temperature drops below 16C but that doesn’t happen very often. At 5:30 the reading was 1.5 bar cold. Yesterday evening it was touching 2 bar fully hot.

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