ASHP - Heating system issues

[LEL]

HI All, i have an LG 14kw ashp powering hot water and central heating in a 5/6 bedroom house approx 350sqm, i have not issues with the hot water side of things, this works perfectly however, the central heating side gives me issues!  when the system works well its great and keeps the house warm but at the moment, once or twice a week the buffer tank which is a 50l cordivari version seems to vent all the central heating system pressure out of of the aav at the top. i have changed the valve a couple of times but still have the same issue, anyone have any ideas what the issue/s might be?

[JohnMo]

Do you close the cap at the top to close the AVV off?

 

Post a pic of what you have and where the issue is.

[LEL]

hi yes, the valve is closed and then backed off a half turn to allow for bleeding automatically, pictures of the offending article is attached now

[Nickfromwales]

The system needs to be flushed and treated, there’s a worrying amount of ferrous oxide present!

This will routinely knacker ever new AAV that you install, so don’t waste time with fitting any more replacements until the cause for their failure is resolved.

I wonder if this was ever treated with inhibitor?!

How old is the system? 

[LEL]

@Nickfromwales thank you for the comment, there does appear to be a lot of build up, i don't think the system was inhibited after installation until just recently, the installer turned out to be an opportunistic cowboy in the end!  the system has been in about 4 years.

 

would you suggest a full heating system power flush, replace the aav, inhibit and then run back up and see what happens?

[Nickfromwales]

1 hour ago, LEL said:

@Nickfromwales thank you for the comment, there does appear to be a lot of build up, i don't think the system was inhibited after installation until just recently, the installer turned out to be an opportunistic cowboy in the end!  the system has been in about 4 years.

 

would you suggest a full heating system power flush, replace the aav, inhibit and then run back up and see what happens?

Ouch....

This will need to be fully chemically flushed to get all the crud out, using something like Sentinel X400 LINK and then a cleaner, and then an inhibitor which I would double-dose with.

 

The killer is, that particular buffer is of steel construction, so without an inhibitor the thing has been rotting away nicely......

Is the system all rads, or a mix of rads and UFH / all UFH?

[LEL]

_{i guess any normal plumber would be able to do this?  i dont need anyone with air source heat pump knowledge?}

 

_{system is a mix of rads and ufh.}

 

_thanks

[Nickfromwales]

3 hours ago, LEL said:

_{i guess any normal plumber would be able to do this?  i dont need anyone with air source heat pump knowledge?}

 

_{system is a mix of rads and ufh.}

 

_thanks

You just need to know the chemicals won’t attack any system components, so check with the manufacturer’s literature before dosing.

 

Any decent plumber can do the job, but you need a plan of attack.

 

The sludge remover needs to go into the system ahead of any other works, and for it to be run up to temp for a good few cycles of ‘chemical flush’, before the system is mechanically flushed.
 

This chemical is supposed to break down the crud and get it into a solution. Then it can be drained down and rinsed out during the mechanical flush.

 

Then fit a new AAV and look back on these happy times and laugh.

[ReedRichards]

39 minutes ago, Nickfromwales said:

The sludge remover needs to go into the system ahead of any other works, and for it to be run up to temp for a good few cycles of ‘chemical flush’, before the system is mechanically flushed.

 

Would you set the heat pump at its maximum fixed leaving water temperature to do this?

[sharpener]

4 hours ago, Nickfromwales said:

The sludge remover needs to go into the system ahead of any other works, and for it to be run up to temp for a good few cycles of ‘chemical flush’, before the system is mechanically flushed.

 

I have used the Fernox citric acid based cleaner for this with good results, need to neutralise well afterwards, don't know if it's still available though.

[Nickfromwales]

On 13/12/2024 at 12:40, ReedRichards said:

 

Would you set the heat pump at its maximum fixed leaving water temperature to do this?

It's down to the manufacturers recommendations tbh, and I have slept MANY times since having to use this stuff last (I only work on brand new installs these days for self-build clientele etc) so if in doubt just read the literature for these products and choose the one that best suits the mix of components and metals etc in your particular system.

 

Just remember to flush it well, a couple of times, and to add in a sacrificial inhibitor each time, even though it's going 'down the drain'. Every time you fill the system back up it is with fresh oxygenated water from the mains and this will instantly start corrosive reactions which is going backwards! Use a cheap inhibitor for sacrificing, and then, when you're happy with the results, drain out for a last time, fit the new AAV, and double-dose with a quality chemical to suit.

[sharpener]

 

On 13/12/2024 at 16:55, sharpener said:

I have used the Fernox citric acid based cleaner for this with good results, need to neutralise well afterwards, don't know if it's still available though.

 

Seems to be, here you are.

 

1 hour ago, Nickfromwales said:

Just remember to flush it well, a couple of times, and to add in a sacrificial inhibitor each time, even though it's going 'down the drain'.

 

The supplied neutraliser provides this function with the DS40. Then inhibit with F1. Other products are available but these have served me well in several houses. Current heating system dates from 1995, last cleaned and inhibited in 2015, HP installers were surprised how clean it still was this summer.

[Nickfromwales]

I have used both Furnox and Sentinel, as said “Tried and tested”…

 

1 hour ago, sharpener said:

Seems to be, here you are.

This is added into the power flush machine, and will do the job if the people doing the power flush are there for the full day leaving the stuff in long enough to do its job. A pour in / rinse out affair is near pointless and would be quite ineffective.

Ask the person flushing to go around and vent the rads etc whilst the machine is in ‘flow’ (the flush machine goes in both directions to stir the shite up most effectively). 

[sharpener]

1 hour ago, Nickfromwales said:

This is added into the power flush machine, and will do the job if the people doing the power flush are there for the full day leaving the stuff in long enough to do its job.

 

Yes or IIRC simply left in the system while running hot as normal for 72 hours, while you get on with something else.

 

Powerflush very fashionable bc it needs expensive equipment and takes time so plumbers can charge more to do it.

 

Edited Sunday at 18:09 by sharpener

[Nickfromwales]

18 hours ago, sharpener said:

 

Yes or IIRC simply left in the system while running hot as normal for 72 hours, while you get on with something else.

 

Powerflush very fashionable bc it needs expensive equipment and takes time so plumbers can charge more to do it.

 

Hire of the kit is less than £100, but some decent plumbers will own one. 
Just get several quotes for duration and costs etc and choose the ‘best’ one. 🤷‍♂️. 
A 1.5-2hp pump will shift a lot more shite than just the heating pump bumbling around