Powermax 155x Pressure Problems

[Billy Whizz]

Hi All

I have a Range Powermaz 155x installed at home and I am having some problems with the central heating. Recently I have found that the pressure is dropping (indicated on the front panel) when the heating is off (the burner is off). I am regularly refilling the system to take it up to the 1bar point. When I say regularly I mean daily or less! Once refilled the burner comes on and the pressure steadily rises to 2.5 bar or there abouts. Once the burner goes off the pressure drops over a short period (approximately an hour or so) down to near 0bar, which can eventually lock the system... I then have to repeat the process so I can get some heat in the house... Now I have looked through some of this forum and the general consencus from people who have faced the same problem seems to be that there is a problem with the expansion vessel.

Now for my question.... If that is the case, which expansion vessel are we talking about? There is the dhw expansion vessel in the unit and also a Zilmet external 18l expansion vessel... Which one is likely to be causing me a problem? How can I check to see if the expansion vessel (which ever one it is) is truly knackered, and if so, where would I go to get a replacement.

I don't really want to call out a heating engineer unless I really have to. Money is a little tight at the minute.

Any help or guidance would be gratefully appreciated.

 

[Alfie-Gee]

I have a similar problem but I don't know how to refill the system?! Ive tried following the instructions but it mentions a secondary tap that I cant find and a rubber hose that I can find!? Any ideas?

 

[Billy Whizz]

Sorry Mate

This is all clear as mud to me... I've opened the front of my boiler and there are various taps inside. I wouldn't know if one of these is the 'second tap' you mention. Maybe someone else will answer both our questions and shed some light.

I can now see the small DHW expansion vessel inside the unit. I just need to know if it is this that is causing me all my problems or the bigger external expansion vessel. Any ideas? How can I test the small expansion vessel?

 

[Onetap]

Now for my question.... If that is the case, which expansion vessel are we talking about? There is the dhw expansion vessel in the unit and also a Zilmet external 18l expansion vessel... Which one is likely to be causing me a problem? How can I check to see if the expansion vessel (which ever one it is) is truly knackered, and if so, where would I go to get a replacement.

The 18 litre Zilmet one.

There is a leak, in that all the water you've added is going somewhere.

It may be caused by the expansion vessel. If the air charge in the expansion vessel has been lost, then the pressure would become excessive as the system heats up, causing the pressure relief/safety valve to open, discharging some water.

Check whether there's water being discharged from the pressure relief valve pipe, as the system first heats up, after you've topped up the water.

To top up the pressure, you need to relieve the pressure on the expansion vessel, then check the air pressure & top up as necessary with a car foot pump. Shut the valves on the CH pump in the boiler whilst doing that, so you won't drain the boiler. If the pressure can't be pumped up, then the diaphragm has failed and you need a new expansion vessel.


The pressure relief valve is set at 3 bar. The pressure gauge may have a 0.5 bar error, or the pressure relief valve spring might be weak. The water contracts as it cools. The pressure should rise to a maximum of 3 bar and drop once the burner goes off.

 

[Onetap]

I have a similar problem but I don't know how to refill the system?! Ive tried following the instructions but it mentions a secondary tap that I cant find and a rubber hose that I can find!? Any ideas?

Should be a flexible connection, outside the boiler.

The hose is connected between the mains and the CH. The isolating valves are opened and the pressure increases. The system should be cold, the required pressure is 1 bar. The hose is disconnected when not in use, to prevent contamination of the mains water supply. This applies to sealed systems, there are open-vented versions of the Powermax.

PS In fact, it's already covered by the 'Sticky' above.
See here;
//www.diynot.com/forums/viewtopic.php?t=38904

 

[Billy Whizz]

Okay...

I've found the discharge pipe outside I think and put a container under it. I've now re-pressurised the system to 1bar on the pressure gauge and switched on the central heating and water. As we speak the pressure is slowly rising (it's at about 1 3/4 at the minute)... I have had a quick look outside and there is a small amount of water in the container (a few mm's)... I'll check again in a minute and keep my eye on the pressure gauge. I'll let you know what happens.

What would I expect if I say, pressurised the system, but didn't turn on the central heating or water? Should the pressure be maintained? What does it indicate if the pressure still slowly drops? I don't know if this is the case I am just thinking of things to try next.

 

[Billy Whizz]

Hi Again

Right, this is what has happened so far. I put a container under the discharge pipe outside and refilled the system to 1bar. I then switched on the heating and hot water and waited. The pressure gradually rose to about 2.5 bar before the burner went off and the pressure slowly began to drop. On checking the container outside I found about 40-50mm of water. When I came back upstairs the burner had come back on, so I turned the thermostat down and the burner went off. The boiler has now been sitting there with no burner on for about 15 mins and the pressure has dropped to about 1 bar.

I guess the next thing for me to do is try to pump up the pressure from the expansion vessel as you suggested. This will at least implicate the vessel as the problem. I can understand now why the system eventually shuts down as it exhausts the water supply by venting it all off over time, and with no continuous feed of cold water it eventually shuts down.

Do you have any idea where I can get a replacement expansion vessel and how much it may cost? It's an 18 litre version. Does it have to be the same make and model or is it OK as long as it has the same capacity?

Thanks for your help so far... it's much appreciated.

 

[Onetap]

Do you have any idea where I can get a replacement expansion vessel and how much it may cost? It's an 18 litre version. Does it have to be the same make and model or is it OK as long as it has the same capacity?

Thanks for your help so far... it's much appreciated.

www.bes.ltd.uk
Item no. 11352

These are Zilmet vessels I think, but another make is OK

It may be a duff expansion valve, if it's dripping at less than 3 bar.
The seat can get scored or they can get grit stuck in the valve If the latter, operating the red easing knob will open it and sometimes blow the grit out; usually a new valve is required.

Don't block the outlet, whatever you do.

 

[Alfie-Gee]

So where do I find the tap to refill? Ive been looking inside the boiler. Could it be elsewhere?

 

[Billy Whizz]

Do you have any idea where I can get a replacement expansion vessel and how much it may cost? It's an 18 litre version. Does it have to be the same make and model or is it OK as long as it has the same capacity?

Thanks for your help so far... it's much appreciated.

www.bes.ltd.uk
Item no. 11352

These are Zilmet vessels I think, but another make is OK

It may be a duff expansion valve, if it's dripping at less than 3 bar.
The seat can get scored or they can get grit stuck in the valve If the latter, operating the red easing knob will open it and sometimes blow the grit out; usually a new valve is required.

Don't block the outlet, whatever you do.

Thanks for the help. However, you've lost me now. Where will I find the expansion valve and what/where is the red easing knob? There is a small red knob on the top of the zilmet expansion vessel.... is that what you mean?

Any help would be gratefully appreciated.

 

[Billy Whizz]

Hi

Can you point me in the right direction for the expansion valve so I can have a look at that before ordering a new expansion vessel.

A few years (?) ago we had a leak in the pipe feeding the expansion vessel which was attributed to a valve in the line. When a Potterton engineer came out he removed this value and replaced it with a blanking nut, stating we didn't need it anyway. I still have the valve, and that has a red knob on top..... is this what you mean when you state 'red easing knob' or am I looking in completely the wrong place?

Cheers for any help.