DIY Doctor

CHVAC and mould and mildew

Postby whatnots2015 » Tue Nov 24, 2020 7:30 am

I live in a rented property and have recently become aware of black spots possibly of mildew appearing inside the house on the external walls and there has always been black mould around a window where the double glazing unit has blown, meaning that there is condensation between the panes. My landlord simply said that I should open the windows more often! Yet last winter I couldn't get the indoor temperature above 15 degrees centigrade even after the heating had been on for several hours. The person who serviced the boiler said that it didn't have a very high output. I suppose my question is, given that the heating system cannot heat the house adequately, will opening windows more often thereby making the house even colder make the mould and mildew even worse? I keep the bathroom and kitchen windows open a fraction all the time and often cook with the back door open as there are no trickle vents or extractor fans or cooker hoods in the property.
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Postby ericmark » Sat Nov 28, 2020 7:14 am

Clearly ventilation is important, however for the boiler not to heat the house enough, really looking for some other problem.

My boiler is 18 kW it does both CH and DHW and the house has 3 floors, 14 rooms, and the boiler is ample. It never runs full time.

I would guess most likely is the lock shield valves are not set up correct, where some one has had problems heating this is common, I will try to explain the likely problem.

Modern boiler are not designed to switch on/off, but are designed to modulate, which means they turn up/down the flame gets bigger or smaller as required.

There are two ways it can do this, a modulating wall thermostat often OpenTherm, which is unlikely, or the temperature of the return water, which is far more likely.

So the sequence of events should be, as each radiator heats up, the thermostatic radiator valve (TRV) slowly closes, and this causes the by-pass valve to lift, and hot water is returned to boiler and boiler reduces flame height (modulates).

Each radiator should have around 15°C to 20°C temperature drop between water in and water out, maybe more, and what happens some one is cold, they open the lock shield valve (The tap other end of radiator to TRV) and the result is the water does not cool enough as it goes through the radiator. Which in turn results in the boiler reducing output, if the heating is never turned off however the TRV for each room will throttle back each radiator as it gets the room warm enough and the heating will still work, it is the re-heat time after any wall thermostat or programmer has turned off heating which is real problem.

First found it in sons house, all lock shield valves wide open, central heating never turned off until Christmas was working fine, but he visited in laws at Christmas so turned off heating and it would not heat up again.

The cure was starting nearest to the boiler turn off the lock shield completely, allow pipes to cool, then turn on 1/4 turn at a time with a couple of minutes between each adjustment until feed pipe just gets warm, then move to next radiator, and do same, this now means each radiator gets a share of the hot water on start up, so all radiators heat together.

Before what was happening was one radiator heats up fully and returns hot water to boiler turning down boiler output, and until that room has heated up, other rooms get no hot water, most TRV heads are marked *123456 which to my mind is useless what we want is 16°C to 26°C as that we can understand, around 3.5 it seems works out at 20°C.

The problem is we have two unknowns, the lock shield valve and the TRV, if the lock shield is set correct, then we can set TRV by trial and error, but if lock shield not set correct, the TRV will likely suffer from over shooting, (high hysteresis) what I did was get TRV heads with °C shown, so that was correct, then I would adjust the lock shield open a bit if cold, closed a bit if hot, but only altering one thing, not two.

If the boiler had a display saying 40% to 100% output you would know if boiler to small or system not set up correct, but that is not the case, the correct setting for lock shield is to measure in and out temperatures, however until Covid 19 when we bought a aim and read electronic thermometer, we simply had no way to read the temperature so could not set it up.
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Postby whatnots2015 » Sat Nov 28, 2020 8:29 pm

Thank you so much for taking the time to write such a detailed reply. Our house has two larger rooms, two smaller rooms and a small bathroom and is generally freezing in winter!
It’s certainly a modern enough boiler to have an automatic pilot light. I have noticed that the radiators have TRVs, all turned up to maximum apart from the broken ones that we cannot move. There seems to be no wall thermostat around the house and the radiators are all warm all over for the whole time that the timing programmer is on. I’ve lived in places before where once the temperature that the wall thermostat is set at is reached, the radiators go cooler or even cold unless they are needed again to warm the place back up to the temperature set on the wall thermometer. We check the temperature using a separate room thermometer.
I will certainly ask the property owner about checking the lock shield valves as I don’t really know what I’m doing and they have a maintenance person for all their properties. We are currently staying at home in self-isolation, and at the moment the room thermometer is saying that it’s 20 degrees. It’s a good thing that we’re enjoying such a mild autumn so far!
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Postby ericmark » Sun Nov 29, 2020 10:32 am

I did not even think about central heating when it worked, only when it didn't work did I start to look at it, and my late mother had a problem, house thrown together 1954 with 4 fires, it was a cold house, so fires replaced with gas versions, and central heating fitted, when dad died it was on second central heating system, and that had clearly been thrown in without much thought on how it would work. The first system was designed for back ground heat only, gas fires used in occupied rooms.

In her case the problem was bay windows catching sun, but this caused me to look at how it can be improved.

What I realised would improve the system was electronic TRV heads, I still have them, as when we sold the house simply unscrewed and refitted originals back on. I spent a lot of money on mothers, but now realise it was not needed, the £10 versions would do the job.

Once the radiator is hot the central heating boiler can't do a thing, so step one is work out if the radiators are big enough, with a modern system around 70°C into radiator and 55°C out, if already that hot only way to get more is a fan, plus then an adjustment on the lock shield valve.

If however the radiators are not at working temperature, then the reheating can be arranged in sequence, this is how it is done in this house, first in the morning, I don't like it hot over night, so the bedroom radiators switch on, then the kitchen, then dinning room, then living room, not much time between them, only 5 minutes maybe but it insures room hot when required. Coming home from work, kitchen, dinning room, living room, then bedroom, if not using room, I only set for background heat.

So I have two temperatures set, varies room to room but we will call then eco normally around 17°C and comfort normally around 21°C and either use a program or push a button to change, I used eQ-3 heads [attachment=0]61dmtMm13BL.jpg[/attachment] I use bluetooth version at £15 each, non bluetooth £10 each, and if you keep the old heads, easy enough to swap back when you leave. No wiring, easy to fit, and they self report faults. So stuck valve you get a fault code, so you know when there is something wrong.

The radiator fans seem expensive, a radiator booster fan costs around £35 and I am considering buying one, cheaper and easier than a new radiator, and again can be removed and taken with you to next property.

What you need to decide is can the landlord fix it, and do you need to fix it?

With the exception of daughters old flat in Frankwell Shrewsbury where the listing resulted in single glazed windows, the owner was not permitted to change them, most homes today has double glazed windows, cavity wall insulation, and loft insulation, seem to remember unless a listed building there are laws for rented property giving minimum insulation? And one can heat a house using just 10 kW, OK not all rooms together in a house this size, but our large living room we have an oil filled radiator as stand-by, in case boiler fails, and 2 kW can maintain the room temperature, as long as chimney is blocked off, and doors closed.

What has happened over the years is old boilers replaced with new, and old boiler could circulate water at 80°C and get whole radiator hot, where new boiler typical 70°C in and 55°C out so it can not put the same amount of heat into the room, but double glazing, cavity wall insulation and loft insulation means not so much heat needed, so the lower output is still normally enough to maintain the temperature, it is things like geofencing where heating linked to phone so only start to heat as you approach the home where you need larger radiators to heat rooms fast.
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61dmtMm13BL.jpg
eQ-3 TRV head
61dmtMm13BL.jpg (65.19 KiB) Viewed 188 times
ericmark
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