ASHP low pressure help pls

[Nickfromwales]

3 hours ago, canalsiderenovation said:

We had not noticed any issue with pressure dropping or leaking tundish til after then so maybe....

....they didn't top back up and run the system to bleed it after topping up the glycol....

 

That's what my money is on if this issue never previously existed, and has now 'gone away'. Will be interesting to hear you report back as it is best to now check it every other week and note any drop. Check it when the system is cold if you can, so the readings aren't of hot (expanded) and then cold (contracted back).

 

 

43 minutes ago, SimonD said:

Needless to say, I'd always test the safety valves. And it is actually a requirement of G3 servicing.

Amen.

[canalsiderenovation]

6 minutes ago, Nickfromwales said:

they didn't top back up and run the system to bleed it after topping up the glycol....

 

I don't think they topped up the glycol, this is on their quote to do with the expansion tanks. They noted the glycol was low.... they are doing it on Friday.

 

The system will be cold (we have not turned the ASHP hot water on since yesterday and won't be turning it on before they come Friday AM. The heating will be off at that time too.

[JohnMo]

A service is supposed to test stuff and then fix and replace items needed. A standard item is test glycol and top up as required. They are also supposed to clean the condenser (finned heat exchanger you fan blows through), clean the casing, inspect expansion vessel pre charge pressure and top up as needed. A cylinder that has got a defective expansion vessel should not be put back in service, as the expansion vessel is a safety item, and be an item to fix asap, as the home owner would no longer have hot water.

 

If you took your car for a service and it came back with a service invoice stating your oil and filter needed to be replaced, and you will need to book that in as it's additional cost, you would be well pissed. That is the service level you have just experienced with ASHP.

[sharpener]

6 hours ago, Beelbeebub said:

Upshot was, there wasn’t anything to "service" - you look at the valve, make sure nothing is blocking the pipework etc and there are no visible signs of leak/degradation. 

 

I have an OSO cylinder fed from a rainwater harvesting system and it suffered from low pressure which I thought was the crap Stuart-Turner pump. Turned out the inlet reduction valve spring had been corroded away by the acid rainwater and was providing no counterforce for the valve.

OSO could only sell me a complete valve block but a 3rd party dealer had a replacement Reliance cartridge which was a lot cheaper.

 

The next fault to come along was the pump, cracked plastic impeller shroud. S-T regard them as unmaintainable but I had the bits of a previous pump which had failed with a leaking shaft gland so was able to fix, no thanks to S-T.

 

Will buy DAB if it fails again, you can get replacement glands for them.

6 hours ago, Beelbeebub said:

 

I asked specifically about turning the knob to activate the valve and he said you could but there was always the risk it wouldn't seal back properly and you'd have a persistent drip, which would mean the valve would need replacing. 

 

Other house has an Ariston cylinder with ?their own valve group which has a mesh debris screeen in it, MIs say to check this annually and I do this though I have never found anything significant in it.

 

+1 for always giving the knobs a twist when I am up there and it is always reassuring to hear the water gurgle away proving the D2 pipe is not blocked with spiders.

[Nickfromwales]

24 minutes ago, JohnMo said:

A service is supposed to test stuff and then fix and replace items needed. A standard item is test glycol and top up as required. They are also supposed to clean the condenser (finned heat exchanger you fan blows through), clean the casing, inspect expansion vessel pre charge pressure and top up as needed. A cylinder that has got a defective expansion vessel should not be put back in service, as the expansion vessel is a safety item, and be an item to fix asap, as the home owner would no longer have hot water.

 

If you took your car for a service and it came back with a service invoice stating your oil and filter needed to be replaced, and you will need to book that in as it's additional cost, you would be well pissed. That is the service level you have just experienced with ASHP.

Yup. Shite service. 

[Nickfromwales]

56 minutes ago, canalsiderenovation said:

 

I don't think they topped up the glycol, this is on their quote to do with the expansion tanks. They noted the glycol was low.... they are doing it on Friday.

 

The system will be cold (we have not turned the ASHP hot water on since yesterday and won't be turning it on before they come Friday AM. The heating will be off at that time too.

Ok. Once the glycol has been topped up, ask them to pressurise when cold to exactly 1.5bar so you can use that as a benchmark to monitor by.

[Nickfromwales]

They’ll have to raise the red vessels, as that’s on fixed pipework, but the white ones are on flexible hoses so make sure that if they just bend the hoses instead of lifting them that the hoses aren’t kinked.

 

If you can ask them to raise the brackets for all the vessels, to accommodate the Tesla valves, then I’d do so to ensure as good job has been done as possible for the fee. 

[Beelbeebub]

I guess the problem with a prv test is a proper test is to stick the immersion on and boil the tank, but that isn't really safe or practical. 

 

The units we had fitted had a knob on the top you turned and that would lift the valve, which isn't really a test of the system only to see if the valve would open. 

 

TBH fitting a burst disc would be the safest way but i've never seen one on a domestic system. 

 

They do need to get around to sorting the g3 regs so that a system only connected to a HP without any immersion can be treated as a vented cylinder since there is no possibility a HP can boil the tank.  That would make installs easier 

[JohnMo]

28 minutes ago, Beelbeebub said:

do need to get around to sorting the g3 regs so that a system only connected to a HP without any immersion can be treated as a vented cylinder

Absolutely out of date nonsense.

 

Just bought an ASHP that does 80 Deg flow temp, unassisted.

[JohnMo]

32 minutes ago, Beelbeebub said:

TBH fitting a burst disc would be the safest way but i've never seen one on a domestic system. 

Too many heat cycles to keep it reliable without regular replacement. Plus some numpy would see a hole in it, and replace with some random bit of metal from the shed.

[Beelbeebub]

10 minutes ago, JohnMo said:

Absolutely out of date nonsense.

 

Just bought an ASHP that does 80 Deg flow temp, unassisted.

Still not enough to boil a cylinder tho? 

 

And if someone fits a co2 HP capable of boiling a cylinder - then it's g3 as per usual. 

 

The exemption would only apply to HPs deemed unable to boil cylinders. Could even be a tick box in the spec where the manufacturer declares the HP unable to reach 95C in all fault conditions. 

[Beelbeebub]

9 minutes ago, JohnMo said:

Too many heat cycles to keep it reliable without regular replacement. Plus some numpy would see a hole in it, and replace with some random bit of metal from the shed.

Good point! The old "nail in the fuse box" fix. 

[JohnMo]

15 minutes ago, Beelbeebub said:

Still not enough to boil a cylinder tho? 

 

And if someone fits a co2 HP capable of boiling a cylinder - then it's g3 as per usual. 

 

The exemption would only apply to HPs deemed unable to boil cylinders. Could even be a tick box in the spec where the manufacturer declares the HP unable to reach 95C in all fault conditions. 

still don't agree, one rule for all appliances, then you don't someone deciding to fit an inline immersion or adding a gas boiler later and then blow their house up. If you want vented rules install a vented cylinder, if you want unvented then G3, simple.

[dpmiller]

with a duff expansion vessel, even 80c could be enough to blow something.

[JohnMo]

1 hour ago, dpmiller said:

with a duff expansion vessel, even 80c could be enough to blow something.

 

5 hours ago, Beelbeebub said:

HP without any immersion can be treated as a vented cylinder since there is no possibility a HP can boil the tank. 

If you treat as vented you may not or wouldn't have an expansion vessel, inlet control group, or PRV. A unvented cylinder is just that, once installed you have zero control what the home owner will or not do. The rules at least make sure that at install stage, a basic set of rules are in place.

[Beelbeebub]

26 minutes ago, dpmiller said:

with a duff expansion vessel, even 80c could be enough to blow something.

Yeah but that's what the usual prv is for. 

 

The tprv for unvented has very specific routing and venting requirements to handle near boiling (potentially above boiling) water partially flashing to steam

[Beelbeebub]

1 hour ago, JohnMo said:

 

If you treat as vented you may not or wouldn't have an expansion vessel, inlet control group, or PRV. An invented cylinder is just that, once installed you have zero control what the home owner will or not do. The rules at least make sure that at install stage, a basic set of rules are in place.

I'm more getting at the routing for the tprv rather than the usual stuff with inlet groups, expansion vessels etc which would all be needed. 

 

I'm coming from the perspective of the annual check needed for a vessel that could potentially explode (though most home owners don't get them serviced). If the vessel can't explode then the safety requirements are less critical. 

 

Actually, while I think about it, given a significant portion of unvented cylinders probably aren't serviced annually, have we ever heard of one exploding? Or even blowing off and injuring someone? I did see a myth busters where they deliberately sealed one shut and boiled it, and it did go off like a rocket. I'd have thought if that happened we'd hear about it. 

[Beelbeebub]

6 minutes ago, JohnMo said:

The rules at least make sure that at install stage, a basic set of rules are in place

Fair point 

[sharpener]

1 hour ago, Beelbeebub said:

The tprv for unvented has very specific routing and venting requirements to handle near boiling (potentially above boiling) water partially flashing to steam

 

But they are ineffective. My installers met all the requirements on paper but the regulation tundish is too small to contain all the splashing. But more seriously, at full flow from the tprv the water backs up in the D2 pipe and would overflow the tundish if I continued the test.

[Beelbeebub]

9 hours ago, sharpener said:

 

But they are ineffective. My installers met all the requirements on paper but the regulation tundish is too small to contain all the splashing. But more seriously, at full flow from the tprv the water backs up in the D2 pipe and would overflow the tundish if I continued the test.

Exactly (this is what happened to us). 

 

In addition, the approved tundish allows a slight trickle of water to track around the support arms to the outside of thr tundish and onto the floor (again also happened) . I modify the tundishes so the copper pipe can drop 10mm or so below the stop o form a drop edge and stop this. 

 

These and various other problems with the venting are what has soured me on UVCs. That said they are neccesary for HPs - the only alternatives are thermal stores, which are inefficient for HPs and vented cylinders, which require pumps. 

 

Which it to explain why I keep thinking some sort of relaxation/rewrite on the regs to make it easier to install and actually work on the rare occasions thry are required to work. 

 

Now all immersion have the double thermostats/cutouts and boilers also have mutiple systems to prevent them boiling the chances of a boiling event are extremely low (though the consequences are still high) 

[Nickfromwales]

12 hours ago, sharpener said:

 

But they are ineffective. My installers met all the requirements on paper but the regulation tundish is too small to contain all the splashing. But more seriously, at full flow from the tprv the water backs up in the D2 pipe and would overflow the tundish if I continued the test.

This is why I always bin the tiny supplied tundish and go from 15mm in / 22mm out, to 22mm in / 28mm out, and have the vertical drop sufficient for the gravity runoff to never back up. 
 

I always add another EV and I always buy my own tundish. Stock supply doesn’t cater for worst case or near-to-ok installation standards (or worse), plus the supplied items are bean-counted to death.

 

Factory EV to the left (400L UVC) and the one I added sits alongside. As this has a hot return there is additional heated volume of DHW outside the cylinder to consider, so I always go nuts on expansion and I don’t get recalls to jobs.

 

Some of my handy work :

 

 

Note, these EV’s all have the splendid Tesla service valves on them   

[Dillsue]

4 hours ago, Beelbeebub said:

These and various other problems with the venting are what has soured me on UVCs. That said they are neccesary for HPs - the only alternatives are thermal stores, which are inefficient for HPs and vented cylinders, which require pumps. 

Why do vented cylinders need pumps? Other than the circulator in the boiler/HP there's no additional pump needed because the cylinder is vented??

[Beelbeebub]

1 hour ago, Dillsue said:

Why do vented cylinders need pumps? Other than the circulator in the boiler/HP there's no additional pump needed because the cylinder is vented??

If you want decent hot water pressure.

 

The vast majority of the properties I look after are flats so the tank is about 400mm above the shower head so the showers are rubbish. 

 

Wasn't a problem 40 years ago when people predominantly had baths but now people expect showers at a decent pressure 

 

(coincidentally we have seen a big rise in bathroom damp/mould issues as showers out in vastly more moisture into the air)

[Dillsue]

15 minutes ago, Beelbeebub said:

If you want decent hot water pressure.

OK, but that's the shower that may need a pump, not a vented cylinder. We're open vented for CH and DHW and have a pump only on an indulgent en suite shower. Rest of house incl a second first floor shower isn't pumped.

[sharpener]

5 hours ago, Nickfromwales said:

This is why I always bin the tiny supplied tundish and go from 15mm in / 22mm out, to 22mm in / 28mm out, and have the vertical drop sufficient for the gravity runoff to never back up. 

 

As installed mine had a compliant 22mm D2 setup taken into a first floor soil stack via a Hep2O bladderless trap.

 

Thinking this was where the restriction was I modified it so there was first a 2.5m drop to the ground floor and the trap went into the stack at that level instead.

 

But it is not much better and will still not take the full flow from the tprv. 

 

So I think that the whole concept that the pipe below the tundish needs to be only 22mm - one size up - is flawed, the regulations do not achieve their aim and are pointless. And a tundish hidden away in an airing cupboard slowly filling with water is NFG either.

 

Personally I think it would be better to have the relief valve piped in 15mm directly to waste with an electrical or mechanical alarm to indicate there is something wrong and possibly a small air admittance valve to vent the pipe but prevent smells. 

 

As a further twist the MCS surveillance visit on another house meant the HP installer was called back to move the tundish to somewhere slightly more visible (even though it was pre-existing and not part of his work). The D2 pipe is 28mm bc of the run length but has a 28mm tundish that will overflow too. So the modification is purely cosmetic, the tundish is still in an alcove off a loft above our bathroom, access is still via a ladder and a door which is kept shut so we will neither see or hear any overflow condition. Which is why I test the tprv whenever I am up there, at least I know it is not stuck and the valve seating is washed clean.