ASHP low pressure help pls

[Russdl]

3 hours ago, ProDave said:

usually indicate the expansion vessels(s) have failed.

How can that be possible in 5 years?
 

I guess only via dodgy installation/commisioning?

[Beelbeebub]

2 hours ago, Russdl said:

How can that be possible in 5 years?
 

I guess only via dodgy installation/commisioning?

5 years is a bit on the short side but I have had multiple ones fail, it's one of the most common things to fail in the heating systems I manage. Prob have one or two a year out of 35 or so. 

 

 

[Nickfromwales]

@canalsiderenovation

 

Don't run back into the arms of these dickheads out of desperation. They've not done a good job here, just perpetuated their revenue stream and kept themselves in business.

 

As part of their visit, they should have diagnosed, not just said "fit a bunch of new stuff". FFS. At the ABSOLUTE minimum, they should have asked to charge you for an hours labour, to check the red vessel pre-charge pressure, to ascertain what is going wrong. The system is too young to have major faults, this is a mountain being made out of a molehill IMHO.

 

The issue(s) is NOT diagnosed well enough yet, so we need to know if the discharged water was warm or hot, and if the heating blew this off or the UVC did. Without this info you, and the aforementioned dickheads, are just flying blind.

 

Leave the hot water on via the ashp and use your showers, you'll be fine for the immediate. Turn off the Solic, even though excess PV at this time of year is negligible anyways, which will reduce the magnitude of the situation.

[Dillsue]

A flip side to the companies approach maybe that the guy that attended for the service is an employee with a set schedule of services to complete in the day with householders taking time off work to wait in for him to arrive. If he gets drawn into doing unscheduled work there's a fair chance he'd mis subsequent appointments and the company would have an unhappy customer or two??

[SimonD]

7 minutes ago, Dillsue said:

A flip side to the companies approach maybe that the guy that attended for the service is an employee with a set schedule of services to complete in the day with householders taking time off work to wait in for him to arrive. If he gets drawn into doing unscheduled work there's a fair chance he'd mis subsequent appointments and the company would have an unhappy customer or two??

 

Okay, so I'm self-employed, but have a run of servicing appointments. As real example of a day, I turn up to my first one and find that the boiler was installed with its prv just sticking out the bottom of the boiler and terminating just behind some boxing in the bathroom. Not safe. So this needs to be dealt with. Next customer gets a text message - I'm sorry I'm running late but there's a safety issue. Arrive at the next customers house to find a shite install where the magnaclean has never been cleaned (even the bleed port is filled with plaster from when the kitchen was done years ago). Then, as I close the service isolation valves on the magnaclean, one of them springs a leak and it becomes apparent that when installed the maganclean connector threads had been damaged so as soon as I touch the thing to take the lid of another leak starts. So next customer gets a text. Then I go to a service where I did the installation and I've made up my time and can pick up my boy from school in time 😉

 

Life in the day of......that's what appointment windows are for ☺️ but every customer was happy to see me, some of whom I'd rescheduled from before Xmas. I find they're pleased to hear if I've found problems and rectify them as that gives them confidence I'll do them same for them.

 

Sorry long ramble.

[Nickfromwales]

4 hours ago, Dillsue said:

A flip side to the companies approach maybe that the guy that attended for the service is an employee with a set schedule of services to complete in the day with householders taking time off work to wait in for him to arrive. If he gets drawn into doing unscheduled work there's a fair chance he'd mis subsequent appointments and the company would have an unhappy customer or two??

And he should / could have used the opportunity to state all of that and book a return visit in. They didn’t. 
 

=💩

[Dillsue]

2 hours ago, Nickfromwales said:

And he should / could have used the opportunity to state all of that and book a return visit in. They didn’t. 
 

=💩

Didn't the company send in a quote for remedial work together with a service report??

[Nickfromwales]

1 minute ago, Dillsue said:

Didn't the company send in a quote for remedial work together with a service report??

They failed to do due diligence, just an assumed 2x dead EV’s at 5 years old. 
 

Sugar coat it if you wish. This is just shit service. 

[canalsiderenovation]

21 hours ago, Nickfromwales said:

Leave the hot water on via the ashp and use your showers, you'll be fine for the immediate. Turn off the Solic, even though excess PV at this time of year is negligible anyways, which will reduce the magnitude of the situation.

 

We can't leave the ASHP on for our hot water. I wouldn't feel confortable to be honest. Water was literally pi$$ing out of the tundish. Someone asked if it was hot or cold but I can't remember. I think cold..

 

28 minutes ago, Dillsue said:

Didn't the company send in a quote for remedial work together with a service report??

 

Yes and no. They did but in the hoo haa of the wrong email/billing issue it went to the wrong email address. I was then able to ask and get this resent which I posted on here.

 

On 11/01/2026 at 18:06, Beelbeebub said:

Which part of the system is that leaking tundish linked to? Is it the domestic hot water or the system loop? 

 

Is there a pressure gauge for the DHW tank?

 

 

Leaking tundish is on our Gledhill water tank. The only pressure gauge I can see is the one on earlier photos and pictures.

 

25 minutes ago, Nickfromwales said:

They failed to do due diligence, just an assumed 2x dead EV’s at 5 years old. 
 

Sugar coat it if you wish. This is just shit service. 

 

I spoke to the company today and have booked them in, hopefully Wednesday. I know @Nickfromwales you will be cursing me but frankly we are stuck. We have visitors later this week and an Airbnb booking so it is a case of sucking it up because the timing could not be worse. We used the gym showers tonight but we dare not turn on the hot water ASHP and have a lot of water coming out.

 

So this is what I am going to ask:

 

1. We want to keep those expansion tanks. Told they need replacing but saw no evidence of this. We want to check them/see this (if they remove them is there a way of checking they have failed if they remove them)? The service form says they need replacing so this indicates they have failed. Do companies routinely replace them or pump them back up??

 

2. We will explain what happened with the pressure dropping to 0, how I topped it up and the leaking tundish. Ask them to check valves are not faulty.

Edited 17 hours ago by canalsiderenovation

[Nickfromwales]

7 hours ago, canalsiderenovation said:

 

We can't leave the ASHP on for our hot water. I wouldn't feel confortable to be honest. Water was literally pi$$ing out of the tundish. Someone asked if it was hot or cold but I can't remember. I think cold..

 

 

Yes and no. They did but in the hoo haa of the wrong email/billing issue it went to the wrong email address. I was then able to ask and get this resent which I posted on here.

 

 

Leaking tundish is on our Gledhill water tank. The only pressure gauge I can see is the one on earlier photos and pictures.

 

 

I spoke to the company today and have booked them in, hopefully Wednesday. I know @Nickfromwales you will be cursing me but frankly we are stuck. We have visitors later this week and an Airbnb booking so it is a case of sucking it up because the timing could not be worse. We used the gym showers tonight but we dare not turn on the hot water ASHP and have a lot of water coming out.

 

So this is what I am going to ask:

 

1. We want to keep those expansion tanks. Told they need replacing but saw no evidence of this. We want to check them/see this (if they remove them is there a way of checking they have failed if they remove them)? The service form says they need replacing so this indicates they have failed. Do companies routinely replace them or pump them back up??

 

2. We will explain what happened with the pressure dropping to 0, how I topped it up and the leaking tundish. Ask them to check valves are not faulty.

No cursing here, just frustrated for you. 
 

As you’re under the gun you’ll want the quickest route obvs.

 

If it’s cold water going out of the tundish then it’s not cut and dry as to what the issue is. The control group (multiblock do-dah that one pipe of the tundish comes from) governs the cold mains pressure to the entire hot and cold system.
 

IF, the water is defo cold then it can mean the cold mains pressure reducing valve has failed, so cold mains water is just being allowed out through the 6bar PRedV, sometimes this will happen sporadically with use of outlets temporarily relieving the issue or network pressure fluctuating.

 

There are 2 places the system ‘blows off’ from, and that’s one. The other is the T&PRV (temp and pressure relief valve) that the other pipe to the tundish comes from, the one high up at the side of the cylinder, usually with a red cap. This operates if the cylinder pressure gets too high, or if the water gets way too hot; bottom line here is, if the hot water is on and the cylinder is hot then the water in the tundish will be the same temperature, eg not cold as you suggest. You’d likely see steam coming off it / out of the tundish if so. 

 

Questions are:

1) was the hot water heated or being heated when you say the cold water was detected at the tundish

 

2) are you sure it was cold?

 

Do consider getting those Tesla valves bought and installed, may be useful to hit different Screwfix’s if one doesn’t have the qty you need in stock, and have these to hand for the chap to fit. Will save you time and money in the long term and they’re quite cheap. These make a proper service / inspection an absolute doddle, and diagnosing issues becomes much easier too, vs having to fully drain down and refill both heating and hot/cold systems every time there’s a need to check / top up the expansion vessels pre charge pressure or identify potential issues etc.

 

Now it’s down to cost and time I guess, but as you’re a rental then I think it’s best to not roll the dice. My 2 cents is to get the 2x cold (white) expansion vessels changed, but to also increase the volume. It seems what you have is not sufficient for this to be long/term reliable, and you don’t want to keep pushing this fault along waiting for it to go again. May as well fix it properly, once.

 

Either change these out for the next size up, or add a third 24L vessel to this setup is my advice. I imagine heating by immersion a lot through summer etc gets this tank super-hot routinely and takes it to its upper limits.
 

Adding more volume is one solution.

 

Setting the temps on the immersion a little lower is another. Eg if you have sufficient hot water during winter from the ASHP, when not heating from solar / immersion, then the temps could be dropped so the safety devices aren’t being pushed to their limit all summer.

 

Without being there I cannot rule out a stray mixer tap back-pressurising the cylinder, but do you know if the cold mains (strictly) only comes in at the plant room and that goes to the control group on the UVC?

 

If both points are so, then the whole house hot and cold supplies should be “balanced”; this is something you could ask the ‘engineer’ when they call out.

 

It’s very easy to just change broken things without finding, or curing, the reason they broke. That’s my concern. 

[canalsiderenovation]

1 hour ago, Nickfromwales said:

Questions are:

1) was the hot water heated or being heated when you say the cold water was detected at the tundish

 

2) are you sure it was cold?

 

Yes hot water was being heated at the time. And no, I am not sure it was cold at all.

 

1 hour ago, Nickfromwales said:

Do consider getting those Tesla valves bought and installed, may be useful to hit different Screwfix’s if one doesn’t have the qty you need in stock, and have these to hand for the chap to fit. Will save you time and money in the long term and they’re quite cheap. These make a proper service / inspection an absolute doddle, and diagnosing issues becomes much easier too, vs having to fully drain down and refill both heating and hot/cold systems every time there’s a need to check / top up the expansion vessels pre charge pressure or identify potential issues etc.

 

Can you send me the link of what is needed and I will order now and ask the guy to fit them. He may not given that they haven't quoted but if it is something he can do at the same time then hopefully it won't be a problem. What do I ask the guy to do, just so I am using the right language when I ask him to do it.

 

Annoyingly I paid the deposit so those tanks have been ordered already.

 

1 hour ago, Nickfromwales said:

Setting the temps on the immersion a little lower is another

 

Is that the temp on the hot water tank? Like the bottom under that white cap, if so we adjusted that a few years ago. Our hot water temp never goes over about 55 degrees. 

 

1 hour ago, Nickfromwales said:

do you know if the cold mains (strictly) only comes in at the plant room and that goes to the control group on the UVC?

It comes in at the utility and all the tank and ASHP stuff is in there so presume so.

 

The Airbnb is a seperate but attached ensuite room to our house so any issues impacts us and them.

[Nickfromwales]

1 hour ago, canalsiderenovation said:

 

Yes hot water was being heated at the time. And no, I am not sure it was cold at all.

 

 

Can you send me the link of what is needed and I will order now and ask the guy to fit them. He may not given that they haven't quoted but if it is something he can do at the same time then hopefully it won't be a problem. What do I ask the guy to do, just so I am using the right language when I ask him to do it.

 

Annoyingly I paid the deposit so those tanks have been ordered already.

 

 

Is that the temp on the hot water tank? Like the bottom under that white cap, if so we adjusted that a few years ago. Our hot water temp never goes over about 55 degrees. 

 

It comes in at the utility and all the tank and ASHP stuff is in there so presume so.

 

The Airbnb is a seperate but attached ensuite room to our house so any issues impacts us and them.

Ask them to supply a 3rd vessel. 
 

The valve is in the first page of this thread with Screwfix part number visible   

[Nickfromwales]

Ask these guys for a full diagnosis of the fault, and why it’s occurred, and the solution. Otherwise you’ll be doing this over and over again. 

[Dillsue]

12 hours ago, Nickfromwales said:

They failed to do due diligence, just an assumed 2x dead EV’s at 5 years old. 
 

Sugar coat it if you wish. This is just shit service. 

It's not sugar coating, it's just a balanced view.

 

Constant slagging of the company/engineer could well cost them work and be the start of a bad reputation if the OP doesn't consider the possible flip side.

[canalsiderenovation]

1 hour ago, Nickfromwales said:

Ask them to supply a 3rd vessel. 
 

The valve is in the first page of this thread with Screwfix part number visible   

 

Got it. Is it just one I need? And where do these need fitting?

[Nickfromwales]

1 hour ago, canalsiderenovation said:

 

Got it. Is it just one I need? And where do these need fitting?

One per vessel, so 1x red, plus 2 (or 3) for the white vessels. 

[canalsiderenovation]

1 hour ago, Nickfromwales said:

One per vessel, so 1x red, plus 2 (or 3) for the white vessels. 

 

Thanks @Nickfromwales

 

Also I did some more troubleshooting. I just turned on the ASHP for hot water. The tundish only leaks when I turn the hot water off. So it heats up fine but then when I turn it off (turned it off at 45 degrees), the tundish starts leaking. It is definately cold water.

[ProDave]

10 minutes ago, canalsiderenovation said:

 

Thanks @Nickfromwales

 

Also I did some more troubleshooting. I just turned on the ASHP for hot water. The tundish only leaks when I turn the hot water off. So it heats up fine but then when I turn it off (turned it off at 45 degrees), the tundish starts leaking. It is definately cold water.

This for me is ringing alarm bells that it is NOT the white water expansion vessels at fault.  If it were then the tank would be discharging on over pressure and that would be 45 degree hot water from very near the top of the tank.

 

I would still want a plumber I trust to test everything and find out exactly what IS at fault.

 

One thing I did when plumbing my own system is I fitted a pressure gauge on the top of the hot water tank so I can see if it is over pressurising.  That is not normally done, but I had one spare.

 

Perhaps when the guys come with their new white expansion vessels you can agree with them, if this does NOT solve the problem they will fit the original ones back and refund that cost?  It is sounding to me like "fault finding by substitution"