Concerned about fix made to pressure on Heatrae Sadia Megaflo unvented system

I already posted a question about this to the MyBuilder.com Ask a Tradesman section but I'm unable to post follow-up questions. Someone has kindly replied that the fix made to my system is dangerous and should be replaced and I'd appreciate it if someone here could validate this advice.

I have a Heatrae Sadia Megaflo unvented system. The water pressure in my flat has decreased over the years and so a plumber replaced what I now know to be the Cold Water Combination Valve (including an attached expansion relief valve connected to a tundish and discharge pipe) with this Pressure Reducing Valve. The PRV isn't connected to the tundish/discharge pipe.

The water pressure is now brilliant again however I noticed that when the boiler is heating the hot water (not the central heating), the gauge on the PRV increases a lot. We have turned down the pressure on the PRV but this isn't a proper fix as surely, the pressure shouldn't increase at all? This feels like a sticking plaster rather than a fix.

What's most frustrating is I bet I could have just replaced the Pressure Reducer Cartridge which would have been much cheaper and less hassle!

I have a few questions:
1) Is it appropriate to replace a Cold Water Combination Valve with a Pressure Reducing Valve?
2) Is the behaviour of pressure increasing when the boiler is running to be expected given the replaced part?
3) Do I need to get the PRV taken out and replaced with a new Cold Water Combination Valve (this looks to be the nearest replacement)?
4) Are there any Cold Water Combination Valves that allow someone to vary the maximum pressure? The pressure used to be so good and if this new valve reinstates it, I'd like to be able to turn it down a little.

Thanks for any advice - I appreciate it!

You should have your system checked over by a G3 qualified engineer as soon as possible.

As a minimum this is to verify that the required safety devices are in place and are operating correctly

Can you post some pictures of the actual installation please. We cannot really comment properly without seeing what you have.

Thanks for such quick responses.

Here are some photos of the original part:



And the replacement:

Yep, that needs changing. Switch it off and don’t use it until it is fixed. I would also probably turn the stop tap off also.

Did the person that carried out the Work hold the G3 qualification allowing them to work on systems like this, based on that repair I would say they probably don’t

Riley said:

Did the person that carried out the Work hold the G3 qualification allowing them to work on systems like this, based on that repair I would say they probably don’t

Click to expand...

The pictures tell me not a chance mate. Looks DIY to me.

Note to the OP it is illegal to work on these installs if unqualified. Also you need the correct parts for the correct cylinder. It’s not just a case of getting best match.

Thread closed. As above, get a qualified G3 registered unvented engineer out to fix ASAP.