Potterton Suprema 100 - H. Sadia Megaflow - problems

[jayessdeecee]

1) Boiler make / model (gas or oil)
Suprema 100
2) What is / is not happening
The pressure on the red tank sited above the Megaflow used to be a constant level just over the 1 bar, occasional topping up was required. HOWEVER over last couple of months the pressure has been dropping to 0.5 bar when the system is idle and then rising to around 2 bar when the system is up and running.
The system has started to make a high pitched whining noise which disapears when I push the lever on the 2 way zone valve over to the left.
All the radiators heat up but there is some fairly heavy knocking in the system when it shuts down.
3) Has ANYTHING else been done / changed recently
Nothing has been added or changed within the system
4) When did it (problem) start
The problem seemed to start about 2 months ago
5) When does it happen? eg, heating coming on or going off
When the heating starts up it sounds as though the pump is straining to push the water through the Zone valve which doesnt appear to be fully opening because the lever is to the right hand side. The radiators get warm but very slowly and then the whining / keening noise starts.
I then push the Zone valve lever over to the left , there sounds like a rush of water , the whining noise stops and the radiators get hot!!!
6) Anything else you feel may be of relevance
There are in the region of 16 radiators, all of them have TRV's and the Towel rail in the bathroom is always on

I suppose my question is - should I consider taking out some Central Heating Insurance, nurse the system along and fiddle with the Zone valve for as long as I can or until it packs in completely or is it something that I need to call someone in for asap before it knackers my boiler or any other expensive component?

 

[shaneo]

ok first thing is 1st, the pressure should never go up, this indicates the diaphramme in the expansion vessle is split, thats the big usualy round thing, that should be on top of the mega flow,
when your boiler is on the pressure will rise, and when it get to a certian amount it will release all the water out the discharge pipe, this is a safety device
the expansion vessle will need replacing

 

[jayessdeecee]

Ok Shaneo , Thanks
But there isnt anything coming out of any discharge pipes or PRV's on the water tank and when the system shuts down the pressure on the guage over the expansion tank drops back down to between 0.5 bar and 1 bar.

Can anyone explain what the Zone valve is doing because it seems that when the system has been running for a while, the lever can be pushed to the left but always returns to the right. What is it that triggers the Zone valve and is it OPEN when the lever is on the left or the right

Is this likely to be an expensive repair

 

[shaneo]

sorry wasnt reading right
if there is never been any water come out the discharge pipe then the vessle is fine,

depending on what valve it is, some of them u can remove the head, use a spanner to turn the valve to the open position, then at least u can see if the system works when the valve is open

 

[ChrisR]

The red vessel is nothing to do with the Megaflo - or shouldn't be. IF your Megaflo has an external pressure vessel, it would be Blue or White. Red ones are not suitable for tap water.

What makeand model of zone valve is it? It isn't Honeywell, they open with the lever on the right.

Find out - with a friend, if the zone valve moves/opens when you turn the heating on. You should see the lever move or feel it move if you take up the free play.

Is there a bypass valve on the system? There should be. Chunky brass valve with a plastic top, and numbers like 0-6 on it. Should connect pump output to return pipe.

Does it make the noise if the hot water is heating up, when the central heating goes off?

 

[jayessdeecee]

Ok, lets see if I can answer some of the questions.
The Zone valve is a ZA-v228/6 Landis and Staefa, the Red (oval shaped) chamber is a Flexcon 18, everything seems to be working - ish, its just that it looks as though the Zone valve is a bit sticky.
My guess is that the Zone valve is open when its on the left because that is the position for 'man open'?

The radiators dont start to get really hot until the lever is pushed over to the left!!

Confused of Croydon!

 

[the boiler technician]

u should have two zone valves with a mechanical spring bypass or a 3 port valve with an auxiliary zone valve in the hot water side. again a spring bypass is required. sounds like 1 or more of the synchron motors are not working or the valves are jammed, which can be open or closed.
check to see if the valve leavers work when on demand and when ALL demand is off the boiler has a pump over run so thats the purpose of the spring valve to allow excess heat to be dumped from the boiler, otherwise it will bang! could event split the heat exchanger.
the boiler technician

 

[kevplumb]

if you go into profile you can add the sig so you dont have to type it every time