TRV's and Boiler Query

[pinheadplanet]

This house never suffers from being too warm. I wish!


Do I need a Gas Safe bloke to install a room stat or is it a simple procedure I could do myself?

 

[D_Hailsham]

What will a Room Stat do for me? We never have the heating on so much that the house gets too warm.

It will turn the boiler off when the house is up to temperature. This will save you gas, i.e money.

Although your boiler has internal controls to shut it down, they are not so accurate as a wall mounted thermostat. This is why it carries on running when it shouldn't.

 

[D_Hailsham]

Do I need a Gas Safe bloke to install a room stat or is it a simple procedure I could do myself?

In theory it need someone with Part P electrical qualifications, not GasSafe. But as it's no harder than wiring a 3 pin plug, you should be able to do it yourself.

You need a thermostat with volt free contacts (most of them are, but you need to check).

The thermostat connects to terminals 1 and 3 in the boiler (remove the existing link).

As you have no thermostat at the moment, it might be easier to install a wireless version as it saves running wires from the thermostat in the hall or living room to the boiler.

The Honeywell DT90E (wired) and DT92E (wireless) are very good.

PS This assumes you already have a separate timer.

 

[pinheadplanet]

Sounds good, looks easy.

I could place one in the hallway and just drill through to the cupboard the boiler is in.

The timer dial is on the boiler itself (see pic)

Thanks

Untitled

• pinheadplanet
• 9 Nov 2010
• 1

 

[D_Hailsham]

I could place one in the hallway and just drill through to the cupboard the boiler is in.

I forgot to mention that you have to make sure that the TRV on the hall rad does not prevent the thermostat working. It can do this if the TRV is set to a lower temperature than the wall stat, as the hall would never get up to the temperature set on the hall stat.

There are three ways you can do this:

Set TRV to max
Remove TRV head
Replace TRV with a manual valve

The hall rad should be adjusted, via the LS valve, so the hall is the last to reach temperature. This will ensure the boiler stays on long enough for all the TRVs to operate.

 

[pinheadplanet]

The Hall is always cold as the rad is only about 2 feet wide!

We always have it on MAX so I guess this wouldn't be a problem, although IF the wall stat never got up to temperature then I guess it wouldn't shut off the boiler would it?

 

[D_Hailsham]

From what you have said about the house never feeling warm, I am beginning to wonder if the heating installation is adequate. This would account for the boiler running for so long.

You need to do three things:

1. Use the Boiler Size Calculator to find out what size boiler you should have. Post this info and the make/exact model of your boiler.

2. Use the Stelrad Elite Catalogue to find the output of your existing rads (add 2kW if you don't know the details for the bathroom ladder rad). Post this info as well.

3. Use Energy Savings Trust Grant Search to find out if you could get low-cost or free insulation.

Please post your replies to this topic

PS On the boiler calculator, the number of front to back walls means those exposed to the open air. So it can be 2 (detached), 1 (end terrace or semi), 0 (mid terrace).

 

[pinheadplanet]

The house has a conservatory. I did a separate calculation for the Conservatory and added it the calculation for the house. However it has a polycarb roof so we might need to add a little to the 'Boiler size required'

The calculations without allowing for the roof are:

Boiler size required: 11.02Kw

Radiators output: 11,149 Watts

Boiler being used is a Halstead Ace High

 

[D_Hailsham]

The calculations without allowing for the roof are:

Boiler size required: 11.02Kw

Radiators output: 11,149 Watts

Boiler being used is a Halstead Ace High

The Ace High can vary its output between 11kW and 30kW, so the required boiler size is at the bottom limit.

The problem is, and this could be the cause of your problem, that you only need this output in the depths of winter, say for a month a year. The rest of the year, when it is not freezing outside, the boiler needs to produce less than 11kW. As it cannot modulate below 11kW, it does this by turning on and off.

And here is where the problem really lies: every time the boiler starts up it goes to max output, 30kW, winds down to 11kW and then turns off again for a time. This means that the system never reaches the required temperature, so the house never feels warm.

The only solution is to change the boiler for one which can modulate lower than 11kW - the lower the better. That is probably not something you want to do.

The reason this problem arises is that most installers and boiler specifiers consider only the hot water requirement when sizing a combi boiler. They ignore the heating requirement completely.

At least the total radiator output is correct and you could install larger rads without the boiler running out of steam.

 

[Agile]

The boiler can only modulate down to 11 kW if the gas valve is set correctly. They can drift with time.

Most boilers can set the maximum power on heating and if thats at maximum the boiler comes on at 30 kW and goes off very quickly.

If the power is set to say 11 kW then it will stay on for longer and give out more heat to the house.

I dont know if your boiler has this setting and I dont remember one but in any case that would ideally be an engineer's adjustment. Someone may look up the book and check for you. Even when there is an adjustment some manufacturers dont mention it in the instructions.

Tony

 

[D_Hailsham]

If the power is set to say 11 kW then it will stay on for longer and give out more heat to the house.

I don't know if your boiler has this setting and I don't remember one but in any case that would ideally be an engineer's adjustment. Someone may look up the book and check for you. Even when there is an adjustment some manufacturers don't mention it in the instructions.

Yes, there is a pot on the PCB for setting the max output - it's mentioned in the Installation Manual. It can be set anything from min to max. It adjusts the burner pressure.

Would be worth getting it done. Get it set to about 14kW

 

[JohnD]

The only solution is to change the boiler for one which can modulate lower than 11kW

Or perhaps increasing the size of the rads?

I did that in my own home so the house warms up faster from cold (I used to go away a lot on business)

That will give more heat to the rooms, helping with the "house never warm enough" problem, and also cut down the short cycling as it will take the boiler longer to get a larger mass of water and steel up to temp. As an amateur, I don't mind having rads that are bigger than a pro would install. I mostly just changed single ones for doubles with fins. If you can do basic DIY plumbing it is also not very difficult to change a short radiator for a long one.

If you have no room stat, yet the house is not warm enough, I presume you are for some reason turning the heating off before the house is adequately warm.

p.s.

The house has a conservatory. I did a separate calculation for the Conservatory and added it the calculation for the house. However it has a polycarb roof so we might need to add a little to the 'Boiler size required'

No, a lot.
A conservatory with a thin roof loses a vast amount of heat. This is why they are supposed to be separated fromn the rest of the house by an external-quality door. You could easily be losing 5kW to 10kW depending on the size of the conservatory and the temperature you try to heat it to.

 

[pinheadplanet]

in Brief,

No- didn't really fancy changing the boiler

I've already added/increased rad sizes to the tune of about about 4kW of rads to the current system!

There's no door or window sealing the conservatory from the main house.

I like the idea of adding even more rads/bigger ones. Even thinking about it is making me warmer already

 

[hi1]

Is it all right to have a stat in a bathroom, electrics steam etc
I was also under the impression that a radiator in the circuit without trv's was to get rid of excess heat in the circuit incase of malfunction, and this was usually the bathroom rad.

 

[Agile]

A stat in a bathroom would be very foolish!

An always open rad is to ensure there is always a flow through the boiler if the otherrads are turned off.

The boiler needs a flow to enable its temperature control to work properly and avoid overheating the main heat exchanger.

We have to fit an automatic bypass to most heating systems now and fit TRVs on all rads.

Tony