ariston microcombi hot water issues

[michael c]

hi guys this is actually advice for my own boiler (i rent my house from family who wont pay for a new boiler). The boiler is a Ariston 23mffi microcombi, in the last 2 years it has had a new heat exchanger, new expansion vessel, tested/replaced thermostat and ndc sensors. The problem only really occurs in colder months, but i have found that the tap beside the boiler gets hot (mixer tap) but the taps in the bathroom only get hot if reduced pressure. The bathroom is only a short distance away however the piperuns travel along a cold wall, under floor with no insulation and then back through a small section of concrete floor which until recently was water logged. I cant get to the underfloor pipes due to tiled floors.
Does anybody think i have missed something or do you agree with me that it is simply the unprotected pipe, incoming temp and undersized boiler (flow rate 9.1l/m but i have a flow rate of 12-13l/m)

Thanks guys

 

[JJ The Plumber]

Sounds like you are losing heat through the uninsulated pipes and possibly running the water too fast.
You said they do heat up if you slow it down at the tap so either continue with this for the colder months or restrict your incoming water to the boiler so it runs at 9.5litres per minute.
The boiler needs time to heat the water that is travelling to your taps, if it's too fast it will only we warm and not hot.

 

[Whn1]

Has it always been like this? Does the hot reach full temp when you run it slow?

 

[michael c]

aslong as i have lived here unsure of before whn1, the hot does get very hot when ran slow thats what makes me think im missing something (i will measure temp diff between sink and bath later) i thought heat exchanger was probably scaled at 1st but got hold of one for free po swapped it which made no difference. I figured it would be due to the piping as cant find fault with the boiler but just thought id check if anyone knew anything that i may have over looked.

 

[michael c]

boiler is reaching 52 degrees at both outlets so guess its not the pipework from boiler. Gas rate is correct, get an anton next week so will be able to check burning properly.

 

[GrahamM]

JJ the plumber is spot on in my opinion.
Different taps, uninsulated pipes and too high a flow rate is accounting for hot water issues.
Common trait of combi's, you need to adjust the flow rate at the taps to give a good, constant flow of hot water. Too fast a flow through a particular tap will result in up and down hot water. The boiler can't keep up.

 

[Whn1]

Can't see it being uninsulated pipes because once they've warmed up it wouldn't be an issue. What taps are in he bathroom? There isn't a blending valve under the bath is there?

 

[michael c]

mixer taps all round mate i did think it was the pipes and flow rate before but now i have tested and the max temp is 52 deg at optimum flow rate at all outlets. I cant see a fault with flame picture and there is no heat passing to the heating side.

 

[dancinplumba]

isnt 52c hot enough ?

 

[michael c]

yeah, just im reducing to around 7lpm to get that mate guess if i want any better i will just have to keep pushing or come to a deal with them for a better boiler (i have offered free installation and supply of everything but the boiler). Its just frustrating when waiting of a bath mate.

 

[dancinplumba]

small combi's crap at filling a bath, carnt you put shower over bath ?

 

[michael c]

got a shower mixer tap mate which is ok. Wife likes a bath though.
Guess i will just have to make do.

 

[dancinplumba]

leave plug in when you shower then she can bathe in it afterwards