hot water scalding, but house not heating past 15 degrees

[bhm1712]

i have a gravity hot water and pumped heating system, with a gloworm space saver mark 2 boiler, grundfos pump, siemens RWB29 programmer and siemens RAA20 room stat.

the room stat never operates because the temp in the house never gets above about 15/16 degrees and i want 19/20, however the hot water is scalding hot.

most of the rads seem hot but its just not warm enougb inside, especially now its so cold outside. i have even turned up the boiler and still no warmer, except the hot water!

any ideas what to do?

 

[Softus]

Likely candidates:

1. Cylinder stat faulty.
2. DHW two port motorised zone valve not closing.
3. Three port motorised zone valve not moving to CH only position.
4. Debris in three port motorised zone valve making DHW port stick open.
5. Auto bypass not staying closed.
6. Manual bypass too far open.

 

[Agile]

Your rads are probably undersized!

You are wasting heat and getting dangerously hot water so adding proper controls would be a good idea.

So new controls and a fully pumped system and some additional or replacement rads!

Its -3.7 °C outside here in NW London tonight but 22.4°C inside!

Tony

Edited to correct the outside temperature from 13.7 ° C

 

[adwt2004]

This is something i'd like to know but would help the OP too I would of thought. How can you find out what rating current radiators are, as in BTU values?

I can't see it written anywhere, is it done on size calculation?

 

[htgeng]

Its 13.7 °C outside here in NW London !

Wow, I didn't think the city effect would have that much of a difference! Its not got above 1c here in East Anglia over the past week. You sure decimal point isn't one place to the left?

 

[bhm1712]

i do not have enough money to upgrade the controls, im stuck with a gravity hot water and pumped heating system for now, ive just moved into my first home so im skint.

there are no motorised valves or cylinder stat its just a basic system, the rads do seem tiny though!

 

[jackthom]

Is the house fairly modern with lots of insulation?

If not, with the price of gas having increased so much, the most economical way of improving things might be a bit of DIY loft insulation and draught proofing.

 

[tonybhoy]

Sounds like the pump is gubbed and the boiler stat out of range.

 

[bhm1712]

the loft has 275mm of insulation all over, and the old couple who lived here before claim that cavity wall insulation was done at the same time, however i have no way of checking this.

draughts mainly come from the front door and windows, although they are double glazed, its just feels cold near the windows.

 

[jackthom]

The insulation sounds pretty good, do the radiators get as hot as you'd expect (top and bottom) considering the hot water temp is so high?

If they're all extremely hot the only way to go is replacing them with larger ones or even just adding extra radiators where possible, perhaps starting with the living room.

 

[bhm1712]

yes they are all hot, i have been around the whole system and bled all the rads, and also had a go at balancing the system.

i will get a couple of double radiators for the coldest rooms, maybe because the room stat is in the hallway where the smallest rad is, it might not be a true heat reading

 

[bhm1712]

question guys,

if i fit a cylinder stat and motorised valve on the cylinder return pipe, when the hot water is up to setpoint the valve would close off the cylinder, would that stop the boiler from heating the central heating system, or blow anything up? because i can see merit in doing that. it would allow me to turn up the boiler to increase rad temperature, but regulate the DHW temp a little more?

 

[Agile]

The whole point of proper controls is to heat the cylinder up to say 55°C and then the valve turns off.

The boiler flow temperature is thus irrelevant to the hot water and can be set to the LOWEST to give enough heat output to the house.

Tony

 

[bhm1712]

i understand

would the method i described work, or would it be problematic? as i can do that diy, rather than have someone come and do it

 

[Agile]

You cannot do that because it would leave the boiler on with nowhere for the heat to go!

It would be highly dangerous.

If you read it up fitting full controls is not THAT difficult if you can do simple wiring from wiring diagrams.

Of course some people who install boilers cannot do it either and have to use an electrician to wire it up.

Tony