DIY Doctor


Postby ishmael1603 » Thu Nov 22, 2012 10:46 pm


We have a house with a THERMflow Thermal Storage Vented Mains Pressure System .

The system is just over x6 years old.

We are finding that the heating in the radiators in the house is fine, but the water in the shower and bath goes cold very quickly. What is this likely to be due to please?

Also the booklet I have here states the following:


The water at the tap is luke-warm or cold.


1. Check that the store is at or approaching 80degrees C. (The temperature is shown on the thermometer). If not, ensure that the boiler/ immersion heaters are switched on. The unit must be allowed sufficient time for the store to reach working temperature.

2. If the valve is turned fully to hot, check that the flow rate at the tap does not exceed 25L per minute. If the flow rate is above this, then turn the tap down slightly.

3. If the store is at or approaching 80degrees C, check that the Thermostatic Mixing Valve is turned to hot. The maximum temperature of water from this valve is 55 degrees C.

I've just turned the Thermostatic Mixing valve as far as it will go to in direction of hot arrow. Why after years would I have to do this? How do you turn the thermostat up as it is in a sealed/ screwed unit? Why after years would you have to do this?

Also I am finding that in our boiler down in the garage Im having to 'top' it up on a nearly weekly basis via the screw inlet water feed. The pressure of the boiler keeps dropping down to 0.5 and I top it back up to between 1 and 2. I thought it was a sealed unit and that you would rarely if ever have to top it up?

Also I've just had a look in the top section of the tank and there is rust/copper coloured sludge in there. I moved it with my hand and the water is now brown.

thanks and look forward to some good advice and help please

Rank: Labourer
Progress to next rank:
Posts: 2
Joined: Thu Nov 22, 2012 10:29 pm


Simply Build It

Postby htg engineer » Sun Nov 25, 2012 10:14 am

It could be one or a mixture of many things.

Firstly if you're losing system pressure daily, you need to find out where the water is going:
- leak somewhere on system
- Pressure relief valve passing
- Expansion vessel has failed

If there's a lot of sludge in the system this will affect performance, the sludge will gather round components etc - in this case it could be round the thermostat sensor/probes meaning it's not reading the temperature of the water correctly.

Shower mixer valves do also become scaled up, if in hard water area and no protection added to the system. The shower valve may require stripping and cleaning or the settings may require altering.
htg engineer
Rank: Project Manager
Posts: 3256
Joined: Tue May 22, 2007 5:22 pm

Postby ishmael1603 » Sun Nov 25, 2012 12:56 pm

Brilliant thanks v much!

I've just ordered some Fernox F4 Superconcentrate Central Heating Leak Sealer (290ml) which Im going to inject through a radiator bleed valve: ... 00_s00_i00

The reviews says its difficult to use, so we'll see. You can apparently inject it via the top up loop fixed to the boiler, which I've looked at home to do on YOUTUBE, but unfortunately like everything in this house when they built it, there isn't small taps in the loop where I can turn the water in the loop off to connect it to the can of Fernox, so I'll have to try and inject into a radiator.

Someone had a look at our tank upstairs and turned the water inlet to the tank off which feeds the pressure and then turned a hot tap in the bathroom on. The blending valve out of the tank to the hot water taps and shower he said has gone and apparently he said that is a common fault. What do you think? He felt the pipes just before and after the blending valve and could feel it hot reaching the blending valve and tepid the other side of it. I'm not totally convinced.

Can I ask should I inject some Fernox Protector and/ or cleaner? Will it dissolve or 'remove' any sludge?
Has the system got to be drained first? My neighbour has a filter on his system now to 'catch' all the sludge if any.

Thanks again
Rank: Labourer
Progress to next rank:
Posts: 2
Joined: Thu Nov 22, 2012 10:29 pm

Display posts from previous
Sort by
Order by

  • DIY How to Project Guides
  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!

  • Related Topics