HELP !!!!!!

Hi ,
We had an problem with our Worcester 49 CDI system boiler just before Christmas .
Basically the fault was the temperature was rising too quick and it would error out .
I did a bit of research and spoke to Worcester and it pointed to the PCB .
Plumber came and assessed and said he thought it was a faulty zone valve .
He told me it would be best to get rid of of the y plan set up and advised to change to an s plan with added expansion for the heating .

We have a tempest pressurised cylinder upstairs .so he got rid of the small water tank in the attic and got rid of the zone valve and added 2 valves ,1 for water and 1 for heating .

Basically , we still had the same original fault .
After several visits I persuaded them to bite the bullet and change the PCB .
This sorted the original issue .
The heating side now seems a lot better ,much warmer and heats up quicker .
The problem now is that we started getting water coming out of the tundish .
After a few plumber visits it turned out to be a faulty new eph zone valve .
The trouble is that before finding this a new incoming control valve was changed and the cylinder tprv , obviously this all costs money .
The bill up to now was around £1300.
Everything seemed fine but I noticed the hot water pressure was crap .
After speaking with the plumber he had turned down the combi valves pressure to 1.5 bar to stop a slight drip at the tundish .
If the valve is turned up to 3bar the water pressure is fantastic but we do get a slight drip .
My reason for posting is that we are still having issues , the heating side is great but the hot water side is very noisy .
Basically when the boilers fires up to heat the tank it sounds like there is a lot of air and there's a lot of swooshing noise , this wakes us up in the morning .
Once the pump is running and things are getting warmed up the pump is making a crackling sound and this wakes us up as well . There isn't anything else to change , they even put a new thermostat in the tank .
Up to now the boiler had a new PCB , tank had 2x new zone valves , thermostat, combi valve , tprv valve and an expansion for the heating .The Grunfos ups pump is brand new .
The only thing not changed is the expansion vessel for the hot water but that's to spec and is only 2 years old
An old air separator was removed and auto air vents added in its place .

Can anyone help or offer any advice as to why we are getting the noisey pump on the hot water side and the sound of air ,it's driving us mad .
The heating side is fine and the pump runs silent when heating is on ,it's when the hot water is on that the noise occurs .
I'm close to getting it all ripped out .
The plumber is G3 qualified .
It's really annoying as the original fault was only a PCB error .
Thanks for any input

Much of your posting makes little sense...

What boiler model is it...no such thing as a 49 CDi. What was the fault code?

Is it really a system boiler? Perhaps you mean a heat only boiler.

It would be most unusual to have an unvented cylinder and Y plan...most installers would not do that and warranty requirements would usually dictate S plan. Perhaps you had Y plan Plus ie. Y plan with and additional 2 port zone valve on the cylinder (although these are rarely wiring up correctly). Part G3 is open to interpretation regarding 2 ports on unvented cylinders.

What is the small water tank in the loft that you got rid of? The Tempest has an external expansion vessel...it must be checked for air pressure annually but it is often prudent to check every 6 months...this is the likely reason for your tundish water dripping.

Why have you got a extra pump if you've got a system boiler..maybe it's really a heat only.

Post pics of the boiler showing the front casing/control panel and GC code, cylinder, zone valves etc.

You're also had a bunch of clueless plumbers so far.

Thanks for the reply .
The boiler was a typo .
Forgive my description I'm a mechanical engineer and this is not my industry .
I'm asking on here because of that .
It's a Worcester greenstar 40CDi conventional.
The pump is next to the cylinder ,I'll post pics .

There was a small f and e tank in the loft that was removed ,it was my understanding that this was for the central heating .
Originally before all the altering we had 1 valve that switched between heating and water and 1 expansion vessel for the hot water side .
Now we have got rid of the single valve and we have a motorised valve for heating and 1 for hot water .
They have also added another expansion vessel for the heating and this does seem a lot better now it has more pressure .

The original fault on the boiler was gradient limitation , replacing the PCB sorted this , apparently a know issue and the board was an earlier spec .
The expansion vessel has been checked and it has 3bar in it .
The boiler has no pump ,it just has a heat exchanger in it .
The pressure reducing valve shown is new ,as well despite the fact we had a new one installed 1 year ago (caleffi) The one in the pic is adjustable 1.5 /3 bar
Thank you for any help

Is the red cap on the aav open at least a turn to let the air out.

Turn off the cold feed to the combination valve, openta hot tap and when the flow stops check the air pressure in the blue vessel.

Get a 1/4 bsp gauge (say 0 to 6 bar) and screw it into the blank port (black plastic plug) on the combination valve. Obviously turn off water first etc. You'll be able to monitor the pressure for better diagnosis.

Isolate the cold to the combination valve and check all cold outlets on mixer valves/showers just incase the cold feed to one of them does not come from the combination valve balanced cold outlet. (It's possible to overpressure the cylinder side via a mixer).

Do you really need 40 Kw ? I'm guessing a lot less.

Thanks for replying .
The auto air vents are open , there are 3 of them
Do I just PTFE the gauge and screw it into the 1/4 BSP hole on the combi valve ?
Can you provide a link to what I need please , sorry to be a pain .
I'll check the vessel tomorrow when I'm back in .
The house is very big and we have 4 bathrooms upstairs so I'm guessing that's why we have a 40kw boiler .
How do I check the mixers , you may of hit on something here as I do remember someone mentioning that some of the bathrooms aren't off the balanced side .
Can a faulty mixer be passing and pressurise the hot ?
So if I isolate the supply to the combi valve and turn on the mixers in different rooms I'll see water still coming out of the taps if they aren't fed from the balanced side ?
We do have really good mains pressure,really powerful .
What would the remedy be ?
Thanks for your time mate
, really appreciate your knowledge

Wrap Teflon tape as a taper.


Your pump/pipework is too small to pull 40kW from the boiler...and most high output domestic boilers need a light commercial setup to get the most from the boiler.

All cold outlets should be taken from the combination valve , if not higher pressure cold can force its way across to the hot side via mixers. Check valves could prevent it but it's a bodge as many mixers need hot & cold at similar pressures for best performance.

Thanks ,
I totally get it now .
There is really good access near the incoming main .
Would it be an option for me to put a PRV valve there so that I know any other bathrooms won't be getting too much cold pressure ?
What is the test to check isolate what appliance could be passing ?
Top advice , thanks for your time

A bodge would be to install a pressure reducing valve just after the incoming main. Ideally you'd just want a single PRV and the non return valve/expansion valve/vessel to take care of the cylinder (years ago unvented cylinder manufacturers would supply combination valve sets that could be split to enable this setup).

Make sure the additional PRV is "drop tight" ie. it maintains the downstream pressure when there is no flow (some valves only regulate under flow).

Isolate the feed to the cylinder PRV and see what outlets still provide cold water.

Thanks , will the valve say if it's a 'drop tight' or not ?
I isolated the valve at the cylinder and 3 bathrooms and the kitchen and utility still had cold water .
They're obviously coming direct from the main .
The gauge I added to the combi valve is showing 4 bar , is that's what's coming to it not going out ?

Cheers mate

Check the datasheet for the proposed valve..