MikeSharp01

Thanks @SimonD I will get some loctite 55 - try and copy the pro's eh.

Yep here are a few. The total depth of the thread in the socket to the lip is 16.87mm the thread length of the barrel plus the washer is 15.76. Also on the return there is no lip more a radius to the pipe diameter inside.

Just tried it and the washer is floating when the barrel is tight and it does not look like it has a flat face at the bottom of the socket just a small lip!

That makes sense going onto the fkt face valve o it's the same for the female set into the machine is it - neat.

I am about to make the final water connections to the heat pump (HP). I want to use a 28mm barrel to the HP connecting to a flat face valve them a swept 28mm bend then onto the flexi to the flow / return pipes running alongside the HP. I was wondering what method to use the joint the barrel into the HP. Liquid PTFE, straight PTFE tape or a more old school method. I prefer the liquid PTFE but am happy to take advice from experts.

Which model is that?

Hopefully! Yes the balance / trade off between flow rate and delta temp I have done calcs based on 3, 5 & 8 K against our limiting UFH (pressure drop wise) loop. Our pump can deal with 7m head and at 3K it will be running at 6.3m head drop.

Technically you are correct the flooring company say 27 but I set the max at 24 in my calculations to see if we could get the output, I think we can, and have a good safety margin - the floor is second only to the windows package cost wise.

Feels way to high for our floor. Got to get my head around this WC thing we need to keep our slab interface to the wooden floor maxed at 24oC so a max water temp of 26 perhaps. What was your floor surface temperature?

So your heat demand should be 10W/m2 or there abouts. Unless you have a huge house or live in the Arctic circle you probably need less than 3kW.

I cannot imagine that the heat pump can overheat the cylinder so I have discounted that issue. My motivation for wiring as it is was just protection for the immersion but also so I could add the PV control later. I looked at the details of your system and thought I might give it a try at some point. There are several other probes in the tank pockets - one for the heat meter, one for the heat pump and one for the BMS monitoring. There are so many safety systems in this system my failure mode analysis (FMA) figured all would be OK. Here are the bare facts: The immersion has a stat of its own that limits the water temperature it can achieve. The immersion has a over temperature cutout should it get that far. The tank has a temperature and pressure safety device. The BMS probe has an upper limit setting that can raise an alarm at a chosen set point (85oC variable) The 24V system has the over temp cutout and the temperature control cutout I could put them in line with the immersion - one or both, but doing so would limit the ability to use all the PV up to 80oC when you wanted only 50oC from the standard cycle. I did consider taking a feed from the immersion live connection, at the immersion and using the BMS logic to tell me if it is powered up when it should be off but have discounted the need for this as the protections above mean it is not really needed. I did figure the Heat Pump would do the whole job but having an immersion as a standby makes sense to me.

I am finalising the wiring for the Heat Pump install and have got to the immersion. When I originally drew up the wiring I had a 24V contactor in the circuit and all the safety / interlocking done on the 24V side to give the BMS full control. Now I am wondering if: a. Am I allowed to have the immersion controlled by a contactor with all the thermal cutout and setpoint control stats in the 24V circuits managing the contactor. (See Image below) b. Should I consider a solid state contactor - if so which? c. What provision should I make for a possible PV diverter, ie terminals below the contactor or what!

Surely the thing about MVHR is that it is controlled ventilation, complimented by heat recovery, and so when combined with great airtightness, which has other benefits in addition, you are in control of the ventilation and the more of the heat that is recovered. You are brining air in and taking it out again in such a way, at such flow rates and in such places that draughts are not a thing, are not subject to the vagaries of the external wind direction / strength. Because it's all warmed so is less obtrusive because it is already mixed and not arriving through very effect venturis that increase its velocity and create discomfort. So it seems to me that, in such a scenario, draughts don't flow freely they flow in a highly controlled manor - it's not pure external air rushing past you to get into the place but air at room temperature flowing slowly past you in from the supply vents and out of the extract vents. It is also, however, clear that the recommendations around the Air Change (AC) volumes is a bit OTT as most people here seem to get by with a fraction of the recommended levels. I started out wondering if MVHR was for us but I have been convinced it is the best way forward and so just allowing air in and out in an uncontrolled fashion is not for us although it would be a lot cheaper at the outset without doubt.

Yes it feels right just to replace all of it. I won't be draining the system down, they will need to wait and get the plumber back for that. I will just run a couple more checks with the heating off later to see if I can hold the water back from cold.

Yes I forced it closed with a spanner and wedged it, left it for a period of 30 minutes no change in temperature.