Baxi platinum pressure keeps dropping off

[Ruggers]

Hi, i have a baxi platinum 33HE, i've been running my existing house on it for 2 years with no problems, ive drained it in the past and upon refilling the system i have no problems with air locks or pressure. I've just built a 2 storey extension and ive added 3 more radiators.

I've joined the extension to the original pipe in the main house and flushed it all, pressurised it and had no problems for 2 weeks. but then after the 3rd week my pressure had dropped to 0.5 (below working pressure) i topped it back up to 1.5 on the gauge and it was fine.

What i did notice was the gauge went up as i opened the filler loop but then seemed to stop and it was as though no more water was going into the system. when i checked on it later on the gauge was showing 2.5 bar which is obviously far to much.

I've left it a week and checked again (week 4) and it was back down to 1 bar when cold. Opening the filler loop only seems to work so far and then the gauge stops. I've been round thwe house 3 times and there are no leaks so any ideas on the promlem? I've even placed a bag on the blow off pipe incase thats passing.

The boiler is situated in the loft and fully lagged & i think has frost protection.

 

[jtc21]

I'd start with changing the PRV and repressurising the expansion vessel, as the pressure has possibly gone above 3 bar at some point activating the valve... and once it's been opened it won't seal properly until it's been cleaned/swapped.

 

[Ruggers]

Would there not be water coming from the PRV if it was passing?, also, why does the gauge seem to stop after so much, i even knocked the boile roff so i could hear if it was still filling the system but it seems to stop flowing, i had a similar problem last year and thought maybe the strainer on the filler loop was blocked but it had loads of flow when i removed one end & opened the valve

 

[jtc21]

It would be dripping yes but sometimes it's at a rate you don't notice. The pressure not going up anymore could be the expansion vessel being flat or could possibly be a blockage. I'd start with recharging the vessel to 1 bar.

 

[Ruggers]

ok i'll try what you've suggested and see what happens, the first time the pressure dropped though the pressure had never been above 1.5bar and had only been topped up a week previous to it. It should be covered under the warranty i think if its the prv

 

[sambotc]

Whats the water pressure like at other outlets?

The increase in pressure maybe due to the extra pipework and radiators added. The extra water will expand when heated causing a higher increase in pressure. You may need to install a secondary expansion vessel to the system depending on the volume of water in your system.

HTH Sam

 

[Ruggers]

What do you mean by pressure at other outlets?

If you mean my hot water taps they seem fine. I've had a bag placed over the pressure relief outlet pipe to see if its passing and nothing is.

I'm running 11 radiators and a towel rail in a 4 bedroom house.

i've left the heating off all day today to see if the pressure drops whist ot running the central heating.

Is it possible for it to be leaking into the condensate pipe or into the heat exchanger and burning off as vapour if the plates weren't tight enough, i really dont have any other ideas, losing over a bar of pressure twice you'd think i'd be able to see damp patches on the ceilings or carpets somewhere

 

[MANDATE]

If you're going to re charge your expansion vessel, do make sure there is somewhere for the surplus water to escape.
I think it is easy to be misled, because it could be charged to 0.8bar yet still be partially filled with water.
Where the air capacity in a vessel has already been reduced, the pressure when compressing the remaining air is going to rise at a much faster rate and will quickly exceed the PRV blow off pressure.
The fact that you have added radiators and increased the total volume of water in the system means there is a larger volume of extra water.
The extra water is supposed to go into the expansion vessel and this itself will mean a pressure rise.
The size of a expansion vessel is matched to the total volume of water in the system, so you have to consider if the size of vessel is still adequate now you've increased the volume
Basically I'm only re-enforcing what Sam has said