High gas bill - Vaillant 637 - UFH and Alu Rads - Help

[Parmsuk]

That's roughly twice the volume of gas that I would have guessed based on your description the house and usage patterns. I'm assuming you're in England not the North Pole, of course.

The two areas I'd scrutinise carefully are:

Firstly, the UFH, in particular what's the specification for the construction of the floor? If there isn't enough insulation under it, or there is two much insulation on top of it, UFH can be a really money-pit.

Secondly, the hot water. How much do you use per day and how is it programmed? Have you got a hot water leak somewhere?

Unless your house is essentially uninisulated or you leave all the windows open the whole time, the amount of gas you are using if it were all dissipated as heating would be baking you all alive. This is why I'm suspcious about the hot water. You might be pouring money down the drain, literally.

There is always the possibility that the meter is faulty and is over-reading. Also, are you sure that your meter is not also supplying a neighbour?

Once you done some basic checks, I suggest you get a heating engineer to do an energy consumption and loss calculation for your house to see how much it should be costing you. They'll also be able to check, approximately, that the consumption rate indicated by the meter matches the rate expected when the boiler is working.

I'm probably repeating stuff others have already because I got interrupted for several hours while typing this answer.

The UFH is set in a 65mm liquid screed, under which is the celotex insulation all to regs and done professionally and then porceline tiles on top. The UFH in this cold weather does take around 2.5 hours in the morning to get to temp, but what I notice is that it rarely comes on throughout the day (monitoring the heat call from evohome) and back on for a top up 30 minutes in the evening.

The hot water is puzzling me to be honest, it was set since we had the system installed (2 years ago) to come on every morning at between 5-6am. But I have turned this off the timer around a week to see if this had any impact. We still have lots of hot water (no one complained that water gone cold). What I have observed is that occasionally the hot water pipe leading from the valve to the tank is hot so this telling me that the boiler is at times automatically reheating??? or is this the tank automatically asking for the water to be heated as its dropped below a certain temperature?

 

[Chuck]

The hot water is puzzling me to be honest, it was set since we had the system installed (2 years ago) to come on every morning at between 5-6am. But I have turned this off the timer around a week to see if this had any impact. We still have lots of hot water (no one complained that water gone cold). What I have observed is that occasionally the hot water pipe leading from the valve to the tank is hot so this telling me that the boiler is at times automatically reheating??? or is this the tank automatically asking for the water to be heated as its dropped below a certain temperature?

You need to look into this and get it sorted. If, for example, the HW zone valve is jammed open you could have a 'hydronic short circuit', which would explain the small differential temperature between flow and return, which will lower the efficiency of the boiler significantly.

 

[gmartine]

Glad Chuck noticed the low differential, as per my previous posts let's see pic's of your set up or we are all Soding in the wind.

 

[Sharp Point]

Have you a secondary hot water circuit?

 

[Parmsuk]

Have you a secondary hot water circuit?

Just checked this morning, there is a dedicated secondary hot water circuit to feed the 5th bedroom/ensuite (furthest away from boiler). Not sure if the mechanical timer was actually in "timer" or "off" mode as it was half way between. Anyway, it was 8.5 hours behind current time (so showing 12:30am at the point I checked this morning). I've ensured its in the off mode and also moved all the little timer sliders to off position so at least I know its for sure not going to come on now. So i'm now wondering if the hot water circuit was coming on early hours of the morning and also again mid afternoon circulating hot water around and actually causing the water tank to cool down? Its during these periods I've noticed that the temp in HW tank drops and then the boiler seems to turn on itself.

I've been monitoring the gas smart meter reading after the heating turns off for the night and again before it turns on in the morning (I know painful). I've noticed consistently that there is at least 10KW used overnight and according to the smart meter the call for gas around 1am and then again at 5am. Once again around mid afternoon of 5KW, all when there is no demand from heating (i.e. target temp is lot lower than current temp).

Lets see what happens today and overnight and I will feed back. Good spot by the way!!!!

So one of my previous question was, if the boiler temperature does drop will the boiler automatically reheat it???? if so whats driving this??? is it the thermostat on the hot water tank?

 

[Sharp Point]

Secondary hot water circuits are energy thief’s, as the pump is circulating the hot water, it’s cooling the cylinder down...as water in the loop is continuously losing heat, the situation would be worse if you had little or no lagging on the pipework.

 

[Sharp Point]

And yes, the cylinder thermostat controls the boiler, you possibly may have a stuck zone valve, that is keeping the hot water on

 

[Parmsuk]

Okay, so I noticed the boiler come back on this afternoon again even though there is no heat demand or timer requirement for HW. So checking the flow pipes to each zone, only the hot water flow was hot which feeds the HW tank. I looked at the boiler stat attached to the tank and it was on 65 (max). I turned it down a bit to say 45 and I could hear the hot water value make a noise (closing??) and then followed by the boiler turning off. It never came back on since...I've turned the stat back to approx. 55C.

So it seems, that regardless of timer settings for HW (which by the way I turned off beginning of Feb to see impact of hot water supply) we have never been without hot water as the boiler keeps it to temp. I wonder if this could also be the reason it coming on middle of the night to reheat the water due to temperature drop?

 

[doitmyself]

So it seems, that regardless of timer settings for HW (which by the way I turned off beginning of Feb to see impact of hot water supply) we have never been without hot water as the boiler keeps it to temp. I wonder if this could also be the reason it coming on middle of the night to reheat the water due to temperature drop?

If you turned the HW off at the timer but the cylinder is still being heated, I would say there is definitely something wrong with the way it has been wired up.

What sort of insulation does the HW cylinder have - none, loose red jacket or fixed insulation? Modern cylinder with fixed insulation will keep hot for many hours. Our one stops heating about midnight and the water is still hot enough for a shower at 10am the next day.

60C is the recommended temperature as it kills of any legionella bacteria.

 

[Parmsuk]

If you turned the HW off at the timer but the cylinder is still being heated, I would say there is definitely something wrong with the way it has been wired up.

What sort of insulation does the HW cylinder have - none, loose red jacket or fixed insulation? Modern cylinder with fixed insulation will keep hot for many hours. Our one stops heating about midnight and the water is still hot enough for a shower at 10am the next day.

60C is the recommended temperature as it kills of any legionella bacteria.

Hi,

Its a valliant Unistore 300l unit.