John Carroll

What is a PITRV?.

I must confess that I thought at first that it might work, if one thinks that a BOE works so well even though one might think that in a pumped system that the hot water might just go straight out the opposite bottom end.

Measuring flow/return temps is generally OK also for calculating rad outputs as long as the plumbing is done correctly, I assisted someone with a HIU system who not only was being overcharged by ~ 30% but was also not getting the required rad output, the heating engineer who came to investigate it insisted that the BTOE system was fine and would work just like TBOE and of course he used the flow+return measurements to "prove" it, to disprove it I piped one of my own rads, below, using both methods, they then plumbed up the system correctly.

Some column rads must have the flow at one particular end because they may have a flow diverter, they may have a arrow somewhere, if not you could try one of these, of suitable length, it force the water up through one column, it will then flow down equally through the remaining 2 or 3 columns. Are they (column) hot along the bottom and cool along the top??.

If the boiler is continuously running at 4.1kWh gas consumption and the output by my calc is 3.924kW then it adds up fairly well as this gives a boiler efficiency of 95.71%. You mentioned somewhere I think that you thought your boiler's minimum output should be better as its not achieving its advertised figure of 3.2kW at 50C/30C, which means the gas consumption should be 3.2/0.9571, 3.343kWh?, what do you reckon is the minimum gas consumption when it starts cycling?

Assuming a average 19.25C room(s) temp and 0.6m3/hr then 21.87kW ofT50s will result in 3.924kW of T13.337s, 17.944% output, but with flow/return/dT of 35.4C/29.77C/5.63C, sounds more reasonable? And for interest if the flowrate is slowed to 0.36m3/hr with 19.25C roomtemps and 35.4C flowtemp then, the output falls to 3.44kW with flow/return/dT of 35.4C/27.19C/8.21C, the difference between 3.924kw & 3.44kW might just be enough to tip the scales into boiler recycle??.

You had a few readings there early in January of flow/return/dT, 35.4C/29.0C/6.4C, by calculation and assuming 20C room temps at I think you said a flowrate of 0.5m3/hr then the rads are 12.199 deg rads with a output of 15.98% and you require a unlikely 23.28kW of T50 rads which will result in a output of 3.72kW, something not right there. if calcs correct, maybe flowrate??

At a OAT of 10C the Targettemp is 23C, the end temp is 29.5C, TT+ 6.5C At a OAT 0f 2C the Targettemp is 31C, the end temp is 32.7C, TT+ 1.7C At a OAT of 10C the burner shuts down at TT+6.5C, is this because its exceeded TT+5C? At a OAT of 2C the burner shuts down at TT+1.7C, why? Does the boiler (FT)ever run at the the TT??.

My understanding of boiler controls then is fairly radically different to the above, my understanding is that the boiler looks at the difference between the target flow temp and the actual flow temp, if the flow temp is < the target temp then the boiler will eventually fire flat out until the flow temp is the same as the target temp or slightly exceeds it, the boiler will then modulate down until the target flow temp and the actual flow temp are almost exactly the same, if the heat demand is < the minimum boiler output then the boier return temp will start increasing which in turn means that the flow temperature will increase until eventually it may exceed the target flow temp by 5C, the burner will then trip, the circ ump will continue to run and the burner will then refire when tha anticycle time has elapsed. Boilers like the Valliant do have return temperature monitoring and if the DT between the flow and return temps exceeds something like 27C/30C will pause the increase in modulation or take some action like this until the dT decreases, their fairly recent system boilers have various pump settings, one of which allows you to set the flow/return dT between 10C and 20C, it achieves this by changing the pump speed which changes the circulation flwrate but does not interfere with the target flow templ/actual flow temp control.

But if you have steady state running and the target/flow dT increases to 5C can only mean that the heat demand is lower than the boiler minimum output?

If the heat demand is/was steady and if the boiler is not at minimum modulation then one might expect a very low target/flow temp dT of max 1 or 2C, I've often looked my daughter's Vokera and its almost allways spot on, biggest dT I've ever seen is 1C. Also, when you were decreasing the targettemp back down to 27C, (from 43C) were you keeping the dT < 5C while adjusting, otherwise the burner should have tripped?.

Even though the targettemp is remotely (weather compensated) set and presumably not jumping around, can/have you set the targettemp manually high enough to ensure the heat demand is slightly higher than the boiler's minimum output to prevent burner cut out and recycling and see does the boiler behave under these conditions, if not, then. IMO, a boiler control problem?. Can you post any trends?

At 00:20:18, boiler modulates to minimum and at 00:21:45 shuts down due to flowtemp being targettemp+5C, isn't this quite normal behaviour??

Here's a dynamic version to check your own systems. Residual Pump Heads Rev1.xlsx

I’ve been asked numerous times to explain the residual pump curves published in some Vaillant Ecotec Boilers MIs, I’ve looked at them several times but afraid I can’t make any sense of them. Someone on here might explain them or/and post similar curves from their (Vaillant) HP circ pump curves, if available. The first screenshot shows my calcs based on a typical 7M circ pump, second screenshot is the Vaillants and the third is unknown but does make sense. The Vaillant’s constant pressure residual default setting is 250mB, 2.5M. At this setting, mine shows a flowrate of 1200LPH (20.0LPM), unknown’s 1300LPH & vaillant’s 1230LPH, much of a much. At 70% pump speed (72% for unknown’s but won’t have any big effect vs 70%) mine = 540LPH (9.0LPM), unknown = 620LPH (10.3LPM), again not hughely different and probably explained by pump differences but Vaillant = 1150LPH (19.2LPM), can’t figure this out but one would think Vaillant have some basis for publishing these figures??. Residual Head.docx