marshian

Really good explanation and makes total sense My Pump is above the cold feed (so 2.0 M plus 3.0 M Head = 5.0 M) so there shouldn't be much chance of air being drawn in - I'll continue my search for why I get occasional slugs of air in the circuits I have turned the pump down from Speed 2 (3.0 M Head) to Speed 1 (1.8 M Head) to try and reduce the system noise and it all seems good on first pass (morning heating - selected rads)

Sorry to thread jack a smidge but thank you for that information - I've got a pump head of 3.0 m but the actual height of the F&E tank water level to the pump is closer to 2.0 m Might explain why I get occasional issues with air in the system with no apparent signs of leaks I think I'll see if I can drop the pump speed and maybe open up the flows thro a few rads to keep the circulation rate the same

Wow that's a heck of a flow rate for a shower - last time I checked ours when looking at water consumption it was 9L per min and I regard that as a decent shower I my concern for our house water usage I did fit a restrictor to reduce the flow to 6L per min and that was fine for me I couldn't notice the difference SWMBO who also didn't notice started whining that it was taking longer to rinse her hair (shampoo and conditioner) so the pump must be going and I should replace it asap................. I timed her showers with flow restrictor and without and it was a tiny reduction in water usage but it did increase the time in the shower by 50% and as I have to wait for her to finish in the shower before I can get in there I decided life was too damn short and I'd look for water savings elsewhere.

I thought that too

Is that the right way round and is it fully open? - stop cock is a fairly convoluted path for water - gate valve (fully open has very little resistance to flow - obv they get a little noisier as you shut them down)

I found using WIser Hub and Smart TRV's I have you could get one rad calling for heat setting the boiler off for a very reduced circuit and a shot while later another rad would call for heat - I think in one particularly cold night I burnt 23kW of gas for no appreciable increase in room temps overnight So I use it to schedule heating periods with a fairly aggressive set back temp at night (almost frost stat setting) this stops individual rads from calling for heat at night What I do like about the Wiser Smart TRV's is they do stay open for a really small trickle of flow and only shut down in the event of a considerable overshoot - so as I'm experimenting with a Weather Compensated flow temp it's actually helped me "tune" the flow thro individual rads especally at the weekend when I have the CH on all day

You have fridge and or freezer? - they randomly top up and cause a spike without you even noticing you are doing anything different. Difference from 0.15p per hour to 0.22p per hour based on say a 35p per kWh for electric is around 200W so it's not enough to be an immersion heater

^ what @Mike said - get a turbo nozzle for the jet wash lance - that makes short work of even the toughest lichen/moss/green

I had a concrete lorry as a garden ornament for a few hours - I'm sure I've got a picture - driver backed it into the garden to shoot a load of concrete into the footings - when it came to driving out he gave it all the beans and as a result dug himself a bit of a hole Ended up pulling it out with chains attached to another concrete lorry

That is a little poor (understatement) PS thanks for sharing the journey

In other news Gas Engineer has had it confirmed from Viessmann that boiler (in current configuration) needs a switched live from the programmer to the boiler - at bloody last!!!

Well my old school plan had a flaw - it wouldn't have been a problem if the gas engineer had used my 3 port valve as I proposed with no mid position in the old airing cupboard arrangement because I only had a bypass fitted for the CH side - HW didn't need one because the flow rate was always far higher (easiest path and all that) However now I have a bypass that will work if pressure in the system is high with CH or HW - closing the gate valve to increase the amount of time the water stays in the coil and reduce the return temp to the boiler is enough pressure to cause the bypass to want to play (By play I mean get involved) So tonight I've been experimenting with pump parameters to see if I can find a pump setting that Provides a min of 0.4 m3/Hr so that the boiler is happy with the level of flow (below 0.4 m3/hr the boiler gets a bit fussy and throws the odd "low flow" fault) when circuit is at it's smallest (ie just one or two rads in circuit) And provides a max of 750 - 800 l/hr (0.8 m3/hr) when all the rads are calling for heat so the boiler can ramp up and get the circuit up to temp Because the alternative plan is fit a NO zone valve in the bypass line so it closes at the same time as the CH NO zone valve........... Anyway no one wants to see a load of tables of what pump results in terms of watts, head and m3/hr is like for 3 different pump operating modes each with 3 different speed settings for both all rads calling for heat and a very tight circuit where I'm left with just two rads still calling (Bypass was closed for this) so I'll just say I've found a setting that meets the requirements but I haven't done HW on it yet.

First question - OK - there probably is an option to change temp or power on a Viessmann 4 pipe boiler but I don't have one of those - I have a two pipe "dumb" boiler with Viessmann "Extras" (actually calling it "dumb" is unfair it's really surprised me with just how clever the program in it is....... I think I've explained elsewhere reasons why I chose the 100-W heat only I couldn't fit a larger boiler in the space I have and hide it in a cupboard I didn't want to run another set of flow and return pipes for the system boiler Only the 100-W has flow and return exiting the boiler at the top (same as my old boiler) So I was pretty much picking what worked best for location and minimal changeover costs I've found a way to rein in the boiler modulation when doing HW, it's a bit old school but it's almost done the job (like everything it's a swings an roundabouts situation - or you could say actions have consequences but I've got a back up plan) Second Question - Temp wise it's 80 deg that's what the boiler targets I have the cyl stat set to 60 deg (it ends up at 63 on a friday legionaires cycle) and that's the only time the cyl stat actually gets to be in control - rest of the time - I have HW set to 20 mins on a timed slot - hence my end of HW temps can vary a little (anywhere between 46 and 54 depending on tank starting temp) but I can live with that. I always heat water before it's needed, I never have a HW demand at the same time as water heating I think the Cyl Stat hysteresis is quite wide - It's just a std Dayton HTS3 probably around 8 deg it also doesn't like being set below 50 deg as it doesn't have a positive off so it's really easy to think you've cracked a position for 45 deg and then find you have no HW because the next day it's Off I don't have an NTS sensor It's how I've always done HW always happy to hear alternatives to my current process but what I do works for us in the house. Sorry probably a bit wordy in reply!!!

So Viessmann Hot water demand box throws 80 deg C at the HW coil and ramps up to 100% Yes water reheat times are super quick but the boiler is quite noisy when it does HW and the tank only really can cope with 3-8 kW without the return temps being 10 deg less than the flow (Old boiler min was 10kW and that gave similar HW times to the viessmann when I ran it at 80 Deg C to get the water done without cycling) So if the boiler modulates based on return temps or flow (or both) Hello gate valve - happy to have you join the party - lets shut you down a little and see what happens 80 Deg C flow - boiler initially hit 100% but as I closed the valve it modulated down to 30% - 20 deg difference between flow and return (76 deg flow 56 deg return) - water heated from 20 deg to 52 deg in 22 mins It was a bit shunty to start with till I found a place where the boiler wasn't overshooting ramping down and then as the flow temp dropped too much throwing much higher kW at the circuit again Basically 1 turn open from closed seems to work fine - that'll do for starters

Gone old school and found a way forward to cap the boilers output - can't stop it going to 80 deg or trying to shove 20kW at the Hot Water circuit with the Demand Box parameters but I'll update that in my Viessmann Boiler thread.

Clarification if I wasn’t clear (I thought I was but apparently not) return pipe hotter than flow when the boiler is “off” I have probes on flow and return pipes after several hours of no boiler activity the temp in the return pipe above the boiler is higher thsn the flow - I believed this was down to thermo circulation - hot moving to cold the addition of s london loop has stopped it “dead”

to round this slight off topic element off - london loop fitted to return from coil - was a right pain to make and fit because of space constraints in the airing cupboard but I normally see 0.66 deg tank loss per hour (it used to be 1 deg per hour before I reconfigured the zone valves) 1900 hrs yesterday - heated the tank to 50 deg - at 8am this morning it had dropped to 46 deg (no major consumption of HW during that time) 0.3 deg loss per hour is an improvement The biggest obvious sign was that flow and return pipes at the boiler were identical - normally I see a higher return pipe temp before I even start space heating I don’t need one on the top of the coil because the zone valve is right next to the coil inlet. I might have to put one on the HW tank outlet now as that’s probably another driver for the losses.

Some spark plugs are 17mm so it shouldn’t be hard to find a box spanner or a spark plug socket - they are extended length

Oh and below is the response from Viessmann technical regarding range rating the boiler (I have another email confirming the same for flow temp max, also adjustable for CH only (not when using HWD box)

Thank you @JohnMo I only really notice the “leaching” when I’ve done the weekly legionaires cycle (an hour or two before some HW is consumed) and when I heat the water much earlier than I need it (like at a weekend when it could be a couple of hours before any water is used) The return side of the cylinder is a bit horrible right now so I’d like to tidy it up and this would be the ideal time to stick a london loop in - even if it has only a small benefit window I might as well put one in

Slighly off topic @JohnMo because I can’t find the thread in question when installing a london loop - does it matter if you have to go up 15cm to then go horizontally for min 15 cm then down for 15cm, across horizontally for 15cm and then up for 15cm? I can’t fit a london loop on my HW tank return without doing this as I’d have to go down into the floor and through a floor joist - if I go up first I can package a london loop easier - it won’t look pretty but it can be done

I asked Viessmann technical help if I could 1. set the max flow temp lower for HW (when demand box was being used) their response was no - it’s preset to max flow temp 2. Use the max output setting on the boiler (range rate effectively) to reduce the kW being used when doing HW (using the demand box) their response was no - this would only impact the CH side the demand box calls for max boiler output and only modulates down when the return temps mean it has too. As a result I shall do what I said I would do earlier in the thread and in none heating months switch back to dumb boiler mode. I will say it’s reheat time is bloody fast - this morning tank was 20 deg C (we’d used all the water yesterday - bath night) and in 18 mins it was 54 deg - I don’t need that speed in the summer 🙂

Because DHWP maximises efficiency on CH but sacrifices a small amount of efficiency when heating HW So when you are using CH the gains on CH running weather comp flow temps out weigh the drop in efficiency when doing HW In the summer you have no need to use CH so I can revert the boiler to non DHWP and run the flow temp at 55 deg C - the boiler runs for 1 hour to get the tank from 25 to 45 (maybe 48 max) it's in condensing mode all the time and the gas usage is lower compared to DHWP when the boiler throws everything at the HW circuit in order to minimise the time spent doing HW and get back to CH asap I've had the opportunity to run the boiler in both modes and I'm pretty sure my data doesn't lie to me. How do you run a heat pump to get the best SCOP or COP - low and slow WC is all about minimising boiler flow temps - keeping the boiler in condensing mode maximises efficiency but to do that and not lose heat in the house you want min down time from heating hence DHWP DMHP for water is actually the exact opposite - chucking everything the boiler has at the HW circuit is not low and slow and there is energy lost to the Flue - why would I want to continue that wasted energy thro the non heating months?

100-W heat only is two pipe - it doesn’t go down as low as the 200 (min 3.2 kW) I’m using a std vented 115 litre copper cylinder (50 mm foam coated) with basic tank stat so doesn’t have the largest heating coil in it (maybe 3kW max) The boiler does modulate down as the return temps get closer to flow but start of cycle it throws everything it has kW wise (rated at 16kW but my readings from the gas meter over a short period of time says everything is just shy of 21 kW 😉 In summer in the installation settings I’ll just switch the boiler back to dumb (B5 then C7 and then select 13 rather than 4 and it’s back to a normal boiler with full control of the flow temps, no weather compensation and no HW demand function) so in a nutshell no wiring changes

I have Viessmann 100W "Heat Only" 16 kW with HW demand box and WC It will raise the tank temp from 25 deg C to 50 Deg C in 15-18 mins with a std vented Cylinder Coil In autumn,winter and spring I will run the boiler with DHWP - I want it done in as short a time possible so boiler gets back to CH running weather compensation at low flow temps Summer when I'm only running HW I will revert to heating HW low and slow as there is a small reduction in gas consumption compared to DHWP when the boiler hits the HW as hard as it can Next year I will look to replace the current HW tank for one with a bigger coil (it should shorten the time for HW in any season but enable the boiler to condense better in summer with a lower flow temp) I will experiment with range rating the boiler because I can't lower the flow temp of the boiler (80 deg C) when it's heating HW - it maybe I can't lower the output either but I'll find out soon enough