ASHP low pressure help pls

[Russdl]

1 hour ago, canalsiderenovation said:

seems we may need to get expansion tanks replaced!

Isn’t it all brand new??

[JohnMo]

4 hours ago, canalsiderenovation said:

That all said we have not had it serviced for about 4 years

 

18 minutes ago, Russdl said:

Isn’t it all brand new??

Doesn't sound like it.

[canalsiderenovation]

1 hour ago, JohnMo said:

 

Doesn't sound like it.

No, it was an RHI install. I think it was 3 or 4 years since our last service to be honest!

[canalsiderenovation]

2 hours ago, ProDave said:

https://www.screwfix.com/p/flomasta-potable-expansion-vessel-24ltr/131kk

 

£40 each from Screweys, so that makes it £310.40 for labour (including the VAT)

 

How long did they say they would take and how many people?

They didn't say but presume just one person. I may get some other quotes or just get it done. Probably the cost of the services we have not had! Just wonder is this likely to be a regular issue or what is the cause of it?

[ProDave]

They should not fail that regularly.  Do you want to do a few checks with us to really determine has it failed, or does it just need the air pumping up?

 

If they do fail regularly it might be a sign they are too small.  What size are the ones there?  We have only seen one of them so far where is the other one?

[canalsiderenovation]

9 minutes ago, ProDave said:

They should not fail that regularly.  Do you want to do a few checks with us to really determine has it failed, or does it just need the air pumping up?

 

If they do fail regularly it might be a sign they are too small.  What size are the ones there?  We have only seen one of them so far where is the other one?

 

It was installed on 8.12.2020. So over 5 years old. Here are some better pictures.

 

[ProDave]

Oh you have 3 in total.  The red one will be for heating, that is your one with the immediate issue. The TWO white ones are for the hot water.  There is no indication that there is actually an issue with those yet.  The fact this guy suggests replacing the 2 white ones but has not addressed the low pressure on the red one has done nothing to give me confidence in him.

 

Lets tackle each separately.

 

The white ones don't have a pressure gauge, they will be at mains water pressure.  They are to take up the expansion when the water in the tanks gets heated.  IF they have a problem, you will see water being discharged via the tundish after you have say had a shower and used up some hot water and the cold water that has entered the tank to replace it is being heated.

 

If you want help identifying what the tundish is, post a picture of the pipework below those tanks.

 

A further note, those tanks are of the type where you can take that bottom flange off and use that access to replace the bladder if it has burst.  But I suspect the labour charge would make that more expensive than just replacing it, if they are faulty.

 

Summary.  If you just accept that quote, you will get 2 shiny new white tanks that may or may not be faulty, and the low pressure on the red one will still be the same.

[Russdl]

25 minutes ago, canalsiderenovation said:

So over 5 years old.

I would call that brand new. Ish.  
 

It looks like @ProDave has got your back to make sure you’re not being scammed. 

[SimonD]

10 minutes ago, ProDave said:

Oh you have 3 in total.  The red one will be for heating, that is your one with the immediate issue. The TWO white ones are for the hot water.  There is no indication that there is actually an issue with those yet.  The fact this guy suggests replacing the 2 white ones but has not addressed the low pressure on the red one has done nothing to give me confidence in him.

+ 1

 

The heating one needs to be tested and it's not always possible to do this at one visit because of the test that are done:

 

1. tank is found at low pressure - you've got to re-pressurise and see how it performs over a few heating cycles

2. If the valve squirts out water when under pressure, this does not immediatley indicate the bladder is shot as it can be condensation build up over the years. So always re-pressurise and see over a few heating cycles.

 

The indication is that because the system has to be de-pressurised and cold to check the expansion vessel pressure properly, it probably wasn't done.

 

But, if the expansion vessel has failed, you will see an increase in system pressure when the system gets hot and this will continue to rise as the system is topped up until the pressure relief valve starts letting by. It's therefore a good idea to check to see if there's any indication of let-by from the heating system prv tundish. The pattern to watch for is - top up pressure, pressure goes down, top up more pressure, pressure goes down until the expansion vessel is completely full and there is no expansion space left, then pressure increases to let by of prv.

[ProDave]

5 minutes ago, SimonD said:

 

The heating one needs to be tested and it's not always possible to do this at one visit because of the test that are done:

That's why I am suggesting @canalsiderenovation does some investigating of her own with our guidance.

[sharpener]

26 minutes ago, SimonD said:

+ 1

 

The heating one needs to be tested and it's not always possible to do this at one visit because of the test that are done:

 

1. tank is found at low pressure - you've got to re-pressurise and see how it performs over a few heating cycles

2. If the valve squirts out water when under pressure, this does not immediatley indicate the bladder is shot as it can be condensation build up over the years. So always re-pressurise and see over a few heating cycles.

 

The indication is that because the system has to be de-pressurised and cold to check the expansion vessel pressure properly, it probably wasn't done.

 

But, if the expansion vessel has failed, you will see an increase in system pressure when the system gets hot and this will continue to rise as the system is topped up until the pressure relief valve starts letting by. It's therefore a good idea to check to see if there's any indication of let-by from the heating system prv tundish. The pattern to watch for is - top up pressure, pressure goes down, top up more pressure, pressure goes down until the expansion vessel is completely full and there is no expansion space left, then pressure increases to let by of prv.

 

All sound advice. Should last for 5 years without probs. Have just taken an expansion vessel out of service as too small for new heat pump. Originally installed in 1995 and still in good working order.

 

As well as the checks outlined above if you get a new one fitted make sure the precharge level is adjusted properly. Mine was left at the factory setting which like yours is 3 bar. This is too high for a system pressure of 1.5 bar and will mean the pv does nothing, the precharge needs to be about 80% of the working pressure as said upthread by ?@Beelzebub.

[canalsiderenovation]

Oh god, sounds like this company do not know what they are doing! For now, I have added pressure back and everything seems to be ok so far. Heating and hot water is on at the moment given the cold snap.

 

I wonder if I am better getting a different company out, explain everything and go from there....

[ProDave]

Just see how it goes for now.  Check next time the heating is off and all cold (first thing in the morning?) and see if the pressure has stayed up or gone back down again.

[canalsiderenovation]

12 minutes ago, ProDave said:

Just see how it goes for now.  Check next time the heating is off and all cold (first thing in the morning?) and see if the pressure has stayed up or gone back down again.

 

It is on during Octopus Cosy times so I will check around 11am tomorrow (it would have gone off at 7am so will have cooled off).

[SimonD]

2 hours ago, sharpener said:

As well as the checks outlined above if you get a new one fitted make sure the precharge level is adjusted properly. Mine was left at the factory setting which like yours is 3 bar. This is too high for a system pressure of 1.5 bar and will mean the pv does nothing, the precharge needs to be about 80% of the working pressure as said upthread by ?@Beelzebub.

 

1 hour ago, canalsiderenovation said:

For now, I have added pressure back

 

Yes, as mentioned check pre-charge, but also useful is there is a system pressure rule of thumb that it's 0.5 bar for single storey dwelling, 1 bar for 2 storey dwelling, and 1.5bar for 3 storey dwelling. Obviously not relevant for now is that most system/combi boilers will stop on an error message below 0.8bar. But some fittings like flow meters require a minimum pressure above this to prevent cavitation.

 

Hence why most installers just put it to 1.5....probably

[Beelbeebub]

3 hours ago, SimonD said:

If the valve squirts out water when under pressure, this does not immediatley indicate the bladder is shot as it can be condensation build up over the years. So always re-pressurise and see over a few heating cycles.

Yes but if the vessel has never been topped up from new this shouldn't be a possibility as they are generally precharged with dry nitrogen - strictly speaking they should only be topped up with dry nitrogen, but nobody bothers. There would only be enough water from condensation to squirt out if it had been topped up a few times, which would indicate an issue somewhere (eg leaking prv) anyway.

[SimonD]

1 hour ago, Beelbeebub said:

Yes but if the vessel has never been topped up from new this shouldn't be a possibility as they are generally precharged with dry nitrogen - strictly speaking they should only be topped up with dry nitrogen, but nobody bothers. There would only be enough water from condensation to squirt out if it had been topped up a few times, which would indicate an issue somewhere (eg leaking prv) anyway.

 

Expansion vessels do lose pressure over time so it's likely it's been re-pressurised at some point, although probably not in this case. And yeah, nobody carries dry nitrogen, or specifies that in MIs for domestic heating systems.

[Russdl]

4 hours ago, canalsiderenovation said:

I wonder if I am better getting a different company out, explain everything and go from there....

I would say stick with experts here (me not being one of them).
 

This is not rocket science and I reckon you can fix/fault find this yourself - with the help of the smart people on this forum -  and then you can either cure your problem yourself, or tell a ‘professional’ exactly what the problem is and what you want fixing. 

[Nickfromwales]

5 hours ago, canalsiderenovation said:

Oh god, sounds like this company do not know what they are doing! For now, I have added pressure back and everything seems to be ok so far. Heating and hot water is on at the moment given the cold snap.

 

I wonder if I am better getting a different company out, explain everything and go from there....

Where was their rationale for the 2x potable (white) vessels needing changing?? Bloody nonsense. At (only) 5 years old they should be fine!

 

Unusual to see two on the hot water, but I always add extra volume on all of my installs, simply as a good measure; you can't have too much expansion afaic.

 

Does the UVC ever heat off the immersion, routinely, as that can seriously over-exert the expansion vessel(s), off solar PV divert etc maybe? If off the ASHP only then these should be living a very easy life, and last e fecking long time.

 

Defo kick these lot to the kerb, and get a new plumber who actually gives a shit.