House not warm enough Vaillant thermocompact 142Eh

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Hunt

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Vaillant thermocompact 142Eh (I know it is old) during this cold weather cannot heat my house enough. Any ideas as to why.

The boiler was checked a while ago... cleaned/gas pressure tested/flame checked for low startup then full flame etc.

Temp gauge says 70 c during this cold weather but it goes higher in the mild sessions we have had.

The actual plumbing of the radiators is the old single pipe with two risers that connect the radiators to the single pipe that runs round the house and back to the boiler.

The system has not changed since we have had much colder winters apart from a towel rail; the towel rail has been connected in the same fashion e.g. using single pipe system with two risers. I cannot see the addition of the towel rail putting much extra load on the CH system as it is throttled to just allow enough water to keep the towel rail warm.
 
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What is the flow and return temperature at the boiler?

That model should be well capable of giving a flow of 80 C.

What position is the rad temperature knob on the boiler?

Tony
 
Hi Tony,
The rad temperature knob on the boiler is max (9)

What is the flow and return temperature at the boiler?
Using an old office wall type thermometer with the bulb touching near the Service cocks, I get 102 f/38 c on the Flow and 74 f/23 c Return.
Can I assume from the above that the Vaillant temperature gauge reads the Return from the radiators? So this explains why the Vaillant temperature gauge will go higher in warmer weather.

What type temperature gauge do you people use?
 
Normally no; I left the heating on all night then they were too hot to touch this morning and the gauge on the boiler now reads 90c
 
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It does sound like the boiler is taking an age to heat the water to 90C. Once there, I Imagine the radiators do their job and warm the house OK?

Measuring flow and return temperatures off the pipe is done with and IR gun or a probe that can be attached to the copper. A traditional thermometer won't get an accurate reading. It could be helpful to have the return temperature, but perhaps not all that helpful.
 
ianniann said:
It does sound like the boiler is taking an age to heat the water to 90C. Once there, I Imagine the radiators do their job and warm the house OK?
Click to expand...
Not really, that's why I'm trying to track down the fault ;)

I've ordered an IR gun so that I can check this sort of stuff and anything else around the house.
 
Hunt said:
I've ordered an IR gun so that I can check this sort of stuff and anything else around the house.
Click to expand...
IR guns will give false (low) readings if pointed at bare copper pipes; painted is OK.

The easiest way of getting consistent readings is to wrap some insulating tape round the pipe and hold the gun against the tape.
 
IR meters are pretty useless except on matt black finish.

Needs a K-Type thermocouple contact meter!

Seems the boiler power output is seriously low.

When was it last properly serviced?

Tony
 
Agile said:
IR meters are pretty useless except on matt black finish.
Click to expand...
The colour is not important. Matt white paint has virtually the same emissivity as matt black. The same is true of insulating tape. It's not the colour which is important but how reflective it is. That's why shiny new copper pipe has a very low emissivity (0.03) but oxidised copper has an emissivity of 0.78. A mirror has an emissivity of 0.
 
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