Flow pipe hot, return cold - is this right

[pistonheadforum]

In the house there are two pipes running up to the 1st floor for central heating - a flow and return pipe. Both are 22mm and this is then tee-ed of to 8mm microbore for 4 radiators and a single radiator on 15mm piping.

The flow pipe is hot and the return pipe is much colder. Is this right? Does this mean the radiators have given up all the heat in the water (presumably good) and returning room temp water? Or should the water be going back with some heat in it so the boiler does not have to keep adding heat?

The radiators in the upstairs bedrooms are giving of a fair bit of heat so I'm assuming this is correct?

Or is this an indication that the boiler should be on a higher setting - it's currently on 1.

What is the most efficient temp delta between the water leaving the boiler and water returning?

Thanks in advance.

Edited by pistonheadforum on Sunday 28th November 12:48

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Thanks very much - boiler currently set on 1 - never changed from the summer.

What do most people run the boiler at over winter - never adjusted it and somewhat scared of a huge gas bill? Maybe each individual system is unique and no one-size-fits-all.

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Is it worth replacing microbore 8mm with 15mm if the rads are all hot? Leave alone or replace the pipework - 30 years old in a soft water area that's recentrly been powerflushed to clear. Planning to rewire so the floors are likely coming up at some point.

I'm guessing 15mm pipe would give of more heat to the pipework (larger diamater means more loss of heat on journey?) leaving less heat for the radiators to release into the room? Or is this not correct.

Would you lag the pipes under the floors or use that to advantage effectivly giving a modicum of underfloor heating?

Thanks in advance.

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98elise said:

Running it higher in winter shouldn't result in higher bills. The heat is still going into the house, just faster and more efficiently. If you run it lower your radiators effectively have a lower output.

Firstly, thanks to all for advice.

This bit has confused me but then I probably don't fully understand I'm afraid.

The boiler is an old non-condensing boiler rated at 80,000BTU. I've converted this and think it's a 23kw rated boiler. It's not particular effeciant with the specs showing SAP of 65% efficiency. Actually that's a horrible effeciency rating.

The boiler is old and not great I get that! I'm trying to make do with the best I have. It has no smart controls.

The setting is currently at 1 and it goes all the way up to a max of 6.

I have 10 radiators in the house over 4 bedrooms with the TRV set low on unused rooms.

Is 1 a bit low?

What does this number relate to? Temp of water? Time boiler is on? How high the flame - is it like a gas cooker oven setting?

Would increasing the number not surely result in a massivly increased gas bill?

Thanks in advance for any light you can shed.

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Thanks.

I've discovered the thermostat/timer is not connected to the system - turning the dial would make no difference and it's been set to over 30 degrees C. Looks like it's been completely cut out the loop and no longer does anything.

However, the boiler is turning it's self off - and back on - and providing heat. What would be doing this? Is this regulated by the boiler in some way and if so where is it sensing this temperature from?

Thanks for all the assistance.

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I appreciate this is all being done blind and who knows how a random system is configured! I'm just keen to understand the principles which I can then apply to my own case.

Many thanks.

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Mr Pointy said:

The boiler has an internal thermostat that cuts the boiler off when the return water temperature gets to a certain point, otherwise it would keep adding heat & boil the water.

If you don't have an external timer how do you control the heating to come on? The stat can be tested by turning it right down when the heating is running; if it's connected the heating will switch off.

It's always on it seems! The hot water tank is wired like a radiator with no TRV so it's always keeping the hot water tank hot. The rooms are regulated based on the TRV (so they do not provide heat in the summer).

Does the temp setting (1) on the boiler determine the temp at which it will turn off and on?

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They system seems to working at the moment but I feel at could all pack in at any moment!

I'm just trying to determine wha the best course of action is until the spring when I a look to get the system inspected and (most likely) the boiler swapped.

I don't want to adjust too much as the bills are managable but the rooms are a bit colder than most - currently 17c or so in the cold spell.

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Mr Pointy said:

Have you got TRVs on every radiator? If so what's possibly happening is that the boiler runs until all the TRVs close off & then the boiler switches off as the return water temperature climbs. When you say "the rooms are cold" which rooms do you mean? If you mean the spare rooms then just turn the TRV up in those rooms. If you mean all the rooms then turn up the boiler water temperature.

A very common arrangement in older systems is a system boiler (as yours is called) that feeds a two way diverter valve that sends hot water either into the HW circuit and/or the CH circuit. There's a stat on the side of the HW tank which turns off the feed to the HW tank when the tank has heated up & a stat in one of the rooms which turns off the feed to the CH when the room is warm enough. It's possible that someone has fitted TRVs to all the radiators & disconnected the CH stat.

Try raising the boiler setting for a few days & see if the rooms are warmer.

Thanks - this is exaclty how it's been configured. It's a heat only boiler with a seperate pump and the CH and HW manifolds have been bypassed so that it's controlled entirely by the TRVs in the room. The hot water cylinder is always passing water as there is no TRV on this "radiator".I guess the boiler going off is because the system gets up to temp (from each room TRV setting), these then close and so the water is being returned to the boiler at enough of a temperature to mean it turns off.

At least I think that's whats happening!

Edited by pistonheadforum on Monday 29th November 09:36

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jet_noise said:

Sounds very reasonable to me. Making the best of an old system for minimum outlay.
Old boilers tend to be very reliable.

When you next have it serviced the tech should measure efficiency. See if it is as low as the 65% figure you've got.
If it really is that low then there is more of an incentive to replace.
You will need to update the control too - at the very least a diverter valve and tank stat. Although you could have that added anyway to the old system.

Thanks. Looking at the system the pump is completly seperate from the boiler (heat only boiler) and is not controlled by the boiler in any way so it's continually running.

Is this likely to be a problem or will it actually put less stress on the system than contually starting/stopping the pump?

Will the pump continually running make any difference to keeping the pipes sludge free?

Thanks in advance.

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bmwmike said:

Agree. I'm not sure it should be diverting via the hot water cylinder though as per OP's earlier post - that could result in very hot water.

It sounds similar to my setup, but someone has chopped some wiring out on yours.

On mine there is an early 90's system boiler, a separate pump and a diverter to send water via the hot water cylinder OR via the radiators OR mid-way so both the hot water cylinder and radiator circuit get heat. I fitted a remote thermostat myself, and that is what turns the boiler on and off for the radiator circuit. The hot water circuit also demands heat and controls the diverter valve at certain times according to a timer. TRV's control room temperature but they cannot tell the boiler to stop heating.

All the magic seems to happen in the wiring box and 3 way diverter valve which has microswitches to control the valve position. I wonder if someone hard wired your boiler for a cheap fix. Wonder if its manually set mid-way.

Exactly this!

The divertor has been bypassed and the water continually goes to both the HWT and the radiators all the time. The TRVs control the heat in the rooms individually. The boiler turns itself off when the return water reaches a certain temp (ie TRVs are shut, water not flowing through radiators, HTW still has heat, in other words the water returning is now still hot as it has not needed to give up any heat).

The pump has been wired to be continually on (I'm guessing this is based on the fact that a pump starting and stopping continually will break faster than one that is just left running?) so the water is continually flowing round the system all the time.

I can't work out if it's pure genius with minimum things to go wrong, or if it needs looking at and modernised? Not broke, don't fix?

[pistonheadforum]

For a 4 bedroom house it's currently on around 35,000 KW per anum for gas. This is with a gas cooker used for cooking.

Leave alone?

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bmwmike said:

I'd be fixing it personally!! I have a large four bed and currently do about 27000 gas a year. You may find the house more comfortable too.

Thanks that's useful information. I'm ooop north in the cold (just incase you are in the warmer south and have an electric oven!)

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From 35,000 to 27,000 is a 22% saving which is roughly £26 a month saving.

That's at current energy cap gas prices though.

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Trustmeimadoctor said:

Why you're bworrying about bacteria in a ch system? If your drinking it your doing it wrong!

Thanks all - guessing meaining that HWT needs to be decently hot if it's indirectly heated.

[pistonheadforum]

Thanks - i'd not thought of that but that makes complete sense! Setting is low to stop the hot water scalding so will be careful about adjusting it as it will increase the temp at the hot taps.

The whole thing needs a refresh I think so planning for this when the weather changes and I can have it off to be worked on.

Reading up a lot of folk talking about unvented systems as the best way forward? Is this right? Surely this would put a bit of stress on the old piping? I'd be reluctant to do this without a compelling reason.

Is unvented more efficient and if not why is the traditional gravity F+E vented not used so much? Is it purely to elimitate the F+E tank in the loft (which I have plenty of space for)?

Thanks in advance to all for advice.