New Radiators INstalled but Still Only get Warm not Hot??


Postby Monkey85 » Tue Feb 28, 2017 7:29 pm

Hi! Really hoping someone can help!

We bought our 1960s house last year and the lounge and hall radiators were always only luke warm. The lounge radiator feeds the hall radiator. The boiler is a Worcester Bosch which is up in the loft and is just over 2 years old and has had a recent service.

We assumed with them being old radiators that they were full of sludge/inefficient etc so we have just had someone come in to replaster everywhere and got them to replace all of the radiators in the house at the same time. (He does plumbing and plastering/general building work)

Every other radiator is boiling hot to the touch and the actual inflow pipe to the hall and lounge radiators are too hot to touch but the radiators are still only luke warm even on full setting. The lounge radiator is hotter than the hall....marginally.

Does anyone have any idea what the problem could be??? Our chap has given up and I just don't understand why the pipe would be roasting but the brand new radiators are only luke warm. There's definitely no air in them and the top of the radiators are hotter than the bottom weirdly.

Could it be a pressure problem?? Any thoughts would be massively appreciated!

Thanks :)
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Postby ericmark » Sun Mar 12, 2017 7:45 am

Likely poorly set lock shield valves, with old boilers they sensed outlet water temperature only, so would run until the output water hit the cut off temperature, so the setting of lock shield valves was not that important, as the TRV closed in each room it would then force water through remaining radiators so in the end all rooms get warm, although being set correct would mean rooms get warm together.

However new boilers also measure return water temperature, this has to be kept cool enough for the condensate bit of the boiler to work, no longer do boilers switch on and off, they alter flame height to keep return water at correct temperature, so if some radiators have their lock shield valves wide open then the hot water returned from those radiators turns down the boiler then turns it off before all radiators are warm.

Start with a hot radiator and turn off the lock shield valve and let the pipes go cold, then 1/4 turn at a time open the valve every 1/2 hour until you get hot water on one pipe, turning down the good radiators will force water though the poor radiators.

Also you should use the thermostatic radiator valves (TRV) to set room temperature not an electric thermostat, the latter is good to turn off whole system as summer comes, but not when you are still heating rooms.

Because the TRV is integrated with boiler using them to control room temperature means boiler turns down rather than off/on so you get a constant even temperature, the electric thermostat will cause a hysteresis with temperatures going up and down all the time, but the TRV will gradually control temperature so room stays at an even temperature.

If you want different temperatures day and night or at different times then the eTRV is the answer, you can set bedrooms only to get warm at night, and living rooms only warm during the day.

However there is a problem, the radiator will not get warm unless the boiler is running, and so to ensure boiler is running you need an expensive system like EvoHome. However you can still use eTRV's but use some thought into programmer setting and/or programmable thermostat setting so ensuring boiler starts up at same time as the eTRV's call for heat. My programmer turns off boiler at 6am and back on at 7am and my eTRV also changes temperature at 7 am so boiler is running.

Some room thermostats are designed to work with eTRV's for example Energenie MiHome eTRV's work with Nest thermostats so they both change temperatures together, not as good as EvoHome but getting close to it an both cheaper and you can add a bit at a time.

The problem with home automation is it's all integrated, so you need wall sockets, light switches, house security and heating to all talk to each other. So in my case I wanted a socket I could switch on/off remotely as well as eTRV's so I went for MiHome as then only needed one hub for both.

In hind sight and hind sight is easy, I think I could have used stand alone eTRV's they did not need to be connected to central hub or be able to control from phone, I have the eTRV set to change at a set time and I never alter it. So a simple timer in the eTRV would have done the job.

My son and daughter-in-law however have house set so when phone is within 10 miles from home central heating auto turns on, and is auto turned off when the alarm is set, they use Nest. For for them the eTRV I have (MiHome) which is a IFTTT device and can follow Nest would be really good for them.

I say this as it's not simply a case of curing one problem, but doing it in a way which will allow at a latter date more problem solving.

I think the room thermostat is the main problem with today's central heating, we have a central heating system designed to use the water both to heat radiators and tell boiler what to do, then spoil it all by adding a room thermostat set too low.

The idea is the boiler heats the water which is pumped around, the lock shield valves are set so with TRV full open each radiator gets it's share of hot water, as each room gets warm the TRV closes, this forces more water through the remaining radiators until so many close that the by-pass valve lifts, until this point the water has been getting warmer on return so flame height has been gradually reducing but with the by-pass valve lifting the return water is too hot so boiler turns off, however clearly the house will cool down again so the boiler has a timer built in, it's called anti-cycle software as it do not have a fixed time but every time it restarts if the water returns too hot again it increases the time before retrying, and if cold then reduces time before retrying so the system maintains the house at a reasonable constant temperature.

This is all well and good in a hospital where you want every room at same temperature 24/7 but in a home we often turn off the system when we are not there, and also we often want the rooms warmer in the evening than in the day, years ago what we did was use inferred heating to supplement the central heating at night, these devices were called tungsten bulbs, however for some reason I fail to understand the government did not like this simple ecological system and banned the tungsten bulb, so this has been replaced by using thermostatic devices which can be programmed to have different temperatures at different times of the day.

So what they have done is required the general public to spend loads of money on their central heating to make it do the same is it did when we used tungsten bulbs, what they seem to have missed is the heat from a tungsten bulb is only wasted when we do not want that heat, when we wanted the heat, then the tungsten bulb was more ecology friendly than the LED bulb, and far better than the fluorescent lamp as they have mercury in them.
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