water pressure through a combi

[terryplumb]

merry Xmas madrab

 

[shambolic]

Not sure I'd agree with that one unless I have picked up the reply the wrong way? Many boilers have flow restrictors contained within the cold inlet that actively reduce the flow into the plate to ensure it can deliver the documented hot water flow rate @ a 35deg rise.

What I was going to say we have s different restrictor for 24/30/35 so the flow rate is regulated to give 35deg rise at 10/12/14 litres per minute.

 

[John D v2.0]

I had one occurrence (it was my son shouting "why's there no hot water") where the bathroom sink hot tap just was running cold. Left it a couple of minutes and it wasn't getting warm at all. Turned off the tap, waited 5 secs, turned it back on and it went hot.

Did you go and look at the boiler at that point?
Probably just failed to start for some reason and basically waiting until next time to try again. We had that in our old flat, sometimes it would just fail to light 3 times in a row and then that was it until the next demand.

 

[chrisw99]

In the op's first post he was asking if the boiler was altering the flow itself based on incoming water temperature to achieve the desired setting ( of hot water from tap) as his flow at hot taps seemed to vary. The boiler does not have such a control function . a flow restrictor does not provide this function .think you have taken my post out of context madrab.regards terry.

Hot water flow was back to it was last evening, and lower again this morning, so definitely seems to be down to local pressure. I need to calculate the cold water flow rate at these times with a jug and a bucket to see how much they change.

The wife had her first bath last night, tap open fully, and it filled up fairly quickly. Certainly better than I was expecting after reading some horror stories about combis. And then she had to add cold as it was too hot as well. I have lowered the DHW temp to 47C at the boiler from the 51 I'd had it.

Could not get a repeat of the basin tap staying cold. Worked every time I tried it yesterday. I know sticky diverter valves can be a common problem, but surely not in a 1 day old boiler. I tried the classic test of running hot water and seeing if the central heating pipes got hot. the first couple of inches did but no more, I guess that's just heat transfer down the pipe.

So far I'm impressed, but then I did have a Halstead Best 50 gravity fed setup that had failed annually and was taking 60-90 minutes to heat up the cylinder to get enough for a bath!