marshian

I have 13 rads - all have TRV's What you describe in terms of leaning on the WC and using the TRV's as temp limiters is exactly what I am doing This is the dining room showing a little solar gain this morning If it his the temp target the TRV will reduce the flow to stop overshoot The dip and recovery was due to water heating stopping the CH for 21 mins (PDHW setup)

Isn't that where you have to accept it as a compromise? I don't want perfection and I can tolerate swings of less than 1 deg (well I say tolerate but what I mean is I can't notice them) I get a small amount of solar gain in Winter in 4 rooms (2 bedrooms, Dining room and Living room) - if the impact warms the room up beyond the TRV set point the rad gets shut down. I'm only running my TRV's now as limiters set approx 0.5 deg above the target room temp. My room to room heat transfer is minimal as the majority of rooms are heated 24/7 (OK to slightly different temps but with say one bedroom at 18 deg next to a bathroom at 21 the delta between them is just 3 deg - there isn't going to be a huge movement with a delta of that size. Heat loss calcs said 22 w gained by bedroom and 64 w lost from bathroom.

Why does do you think it tries to go up the vent The level of water in the vent is the same as the level in the tank - it has to be The only reason the vent pipe (and the cold feed) get warm is convection It will pull water from the cold feed under certain circumstances - when you have a leak in the system or bleed a radiator that has a lot of air in it. Rest of the time it's a static head above the pump Water expands when heated - the tank provides a safety element allowing water volume changes due to temp to be accepted without causing system pressure changes When the system cools the volume increase in the tank is given back to the circuit

So the problem is either blockage in circuit or Pump Head exceeds system design As you've recently changed the pump my money is firmly placed on the Pump "Settings" being the cause of the pump over PS I was hoping @John Carroll would join this thread - he was very helpful in explaining my system issues and as soon as the spring is here I'm moving to a combined vent and fill

I can understand the concerns but studies have shown that the risk of catching Covid from physical items is very low - the risk is mainly airborne and close contact with someone who has the virus is probably the biggest risk Transport for London have long since abandoned the hand sanitiser stations https://tfl.gov.uk/transport-accessibility/cleaning-and-air-quality You do you but if you haven't had Covid 19 already I'm amazed and you've done very well to avoid it. I seriously doubt that wiping everything you come into contact with with sanitiser is going to make the slightest bit of difference to your chances of catching it. I had Covid in November 2019 - an unintended consequence of a holiday in North Vietnam on the border with China or migrating thro two large airport hubs I was never sure where I caught it It (the original strain) was proper nasty and I wouldn't recommend it to anyone but a virus that kills it's host doesn't tend to last long - it's evolved into a much less aggressive strain over time Not had it since either - the human species is quite amazing in it's ability to deal with pathogens that it's had to meet.

With HW demand box it's not possible to cap the boiler output on HW mode (Viessmann Technical told me this when I asked how to stop the boiler throwing 19kW at a 3kW HW coil) I know on CH it is possible and I know 10.6% is my boiler min (3.2 kW in low temp operation) because I've measure consumption at that rate in long stable burns. I did a little study a while back on HW to see what the boiler was really kicking out 100% is 19 kW (on a 16kW rated boiler - go figure) 50% is 10 kW 33% is 7.4 kW So I've set it to 20% and see if that stops the issue but still gives me some head room on restarts

How bloody right you are - today was 11.5 Deg C - flow temp target on the WC curve was 26 deg Cycling wasn't great - rooms maintained temps but at the expense of frequent short burns over 30 burns so far today I think the driver is the flow temp rises too fast for the boiler to modulate down rather than the circuit being too small I increased the room temp target to 25 which skews the WC curve to be 34 at 10 deg C and got a couple of decent length burns at the expense of room temps bouncing of the TRV temp ceiling I'm going to range rate the boiler to 5kW (or whatever % that works out to be) and see if that fixes the issue

Here's my math for my rad sizing In a nutshell what I had was a calculated heat loss at -2 and a rad kW output at T50 - what I wanted to see was where as I stepped down flow temps was I likely to have a problem with rooms not meeting the target temp (ie the rad was borderline) In truth I think my heat loss parameters for ACH and loft losses were a little pessimistic and so my heat losses for some rooms are a little higher than reality. But it does show clearly that I am likely to have an issue with three or four rooms

It's actually I think hard to match rads to exactly the room heat loss requirements and not get them oversized (OK I did in one room) For 95% of the year they are oversized by virtue of the outside Air Temp being above the worst case outside temp. Pretty much agree with that

My other half and her mate bet on every single horse in the Grand National once......... 2009 was a lucky year for that process 100/1 winner

If rads are also oversized then you can reduce the flow thro that rad at any given temp and basically make it behave like a smaller rad Quite hard to go the other way mine except winding up the flow and sacrificing the return temps I can definately save some gas by turning the heating off when I'm not in the house but the re-heat process means I have to start quite early before I get home and I'd rather have the house heated a little lower all the time than burst of high energy heating I think there is a lack of clarity in the discussion but you only get clarity by discussion so lets keep it going in the good natured way it is World is too damn polarised now Exactly what I mean by polarised viewpoints - there is no right and wrong only different approaches (with the UK's housing stock - there is an awful lot of grey and I'm not talking about the fashion trend for windows and cladding)

If I hadn't done the math @SteamyTea would have but he'd have used Joules or some other unit of measure 😉

Quick bit of maths 300 L tank heated to 85 Deg C You only use 250 Litres so 50 litres remain at 80 deg after 14 Hrs (Assumption is minimal losses) That 250 Litres has been replaced by 250 litres at 10 Deg temp (It's winter average delivery temp) So you've got 250 litres at 10 deg and 50 Litres at 80 deg If you mixed them you get 300 Litres at 21.6 deg C The mixing occurs when you turn an immersion on that's in the side or the bottom of the tank

Yes they do work differently - it's called stratification The hot water stays at the top of the tank and loses a small amount of temp due to tank convection losses - it's replaced by incoming water at anywhere between 5 deg and 20 deg depending on the season - there is minimal mixing between the two You heat a well insulated UVC to 85 deg C you are probably going to get 80 deg water out of it after 14 hrs until you hit the boundary layer then you are going to get 5-20 Deg water - like a switch!!!

300 L to 85 Deg C from say 20 Deg C only uses 15kW of electric? If the tank is being fully consumed daily and it sounds like it will be with that level of occupancy then to get 300 Litre of water from 20 Deg C to 85 Deg C is going to need a heat input of 22 kW So by my rough math your calcs are understating you usage by 45% With a 3kW immersion it's going to take 7 and a bit hours which is quite a chunk of time to recover

I'll take that as a compliment 😉 Background - for my last 40 years in work I've been a data analyst - it's really bloody hard when you are good at working with data to ignore it in a home environment. Basically if I can't validate something with data then it's a guess or a hunch and I don't do either of those

I'm reminded of the ultimate race horse designed by a committee Yes I know camel racing is a thing but that's not the point I'm making

I'm clearly not most people Below is my daily gas usage and below that my HDD data both by day for December Pretty clear to me my heating consumption of gas is driven by the outside temp and there is a close relationship

Just for comparison When I have my heating on I have 1 circulation pump running at 15W Boiler and Control system consuming 55W (when running) No Zone valves powered up at all (NO zone valve for CH) Only when I do HW do I have a zone valve energised for 21 mins a day.

My octopus app says I used 8% more gas this last week 33.9 m3 than the previous week 31.4 m3 The local weather station HDD says last week was 74.9 HDD The previous week was 64.9 so 15% colder I'm going to chalk that up as a win

I think you may miss a slight but subtle difference in the conversation In my case I'm not trying to nail room temps to a 0.1 deg difference - I'm quite happy to accept a slight over or under over 24 hrs I'm not controlling room temps with TRV intervention - I'm only controlling the boiler flow temp to maintain the room temps in the target area. As a result circuit size doesn't change - the TRV's remain fully open and I'm using all the 150 litres of water in the CH circuit acting as a nice buffer for heat distribution to the rads If I was running the same process using an elevated flow temp and was reliant on TRV's to manage the room temps the circuit size could be anything from 2 rads to 13 rads. This is what I believe would be a wasteful approach in terms of energy because the boiler would cycle like a bitch in shoulder months as my heat loss is 4.7 kW at -2 and the min the boiler can get down to is 3.2 kW so at 10 deg C outside my heat loss is probably 2.2 kW If my CH heat circuit was down to 2 rads the boiler would be cycling like crazy pissing energy out of the flue as the kW input would be massively over sized for the circuit volume.

If they don't have threaded inserts in the base - pretty much any damn self tapper will resolve that!!!

https://surewayheating.co.uk/products/new-003051-stat-cl6po134-genuine-spare I wouldn't mind betting the only difference is the length of the capilary tube and if the one above is 134 mm and your original part is 117 mm

I don't think a little thread jacking hurts - it was an old post resurrected anyway PS I'm finding the discussion really interesting

Exactly - we are not talking about wasteful overheating of rooms (ie more than the heat loss of the room) but carefully matching the loss - now that may mean constant operation but at much lower flow temps I'm far more comfortable in a room constantly heated to 19 deg C than I am in a room which is heated to 21 deg when occupied and loses 5 deg overnight The energy required to get the room back to temp is only slightly less than the energy required to keep it at a constant but lower target temp Agreed - as stated elsewhere - condensing boilers were mandated but not the adoption of lower temp emitters which were essential to get the boiler efficiency improvements from the condensing mode they were designed to run in. Effectively condensing boilers were installed and then run at the same flow temps as the old non condensing boilers - it doesn't get more stupid than that!!!