Help needed - possible Boiler thermostat problem

[EmJayDee]

Hi all,

I'm new to the forum, and am a complete plumbing novice.

I've been reading the forum for about a month trying to find out what's wrong with my heating - but so far I haven't been able to identify a solution to my problem.

The system is relatively new (about 10 years) with micro-bore pipes, and comprises:
- Ideal Classic FF280 boiler (GC 41-387-06)
- Grudfos UPS 15/60 pump
- 2x Drayton ZA5 zone valve actuators
- 17 radiators
- Horstmann DRT2 programmable electronic room thermostat

For the past few months, the system has been overflowing from the F+E tank in the loft, seemingly at random intervals, and it's now getting rather annoying.

A heating engineer did come and have a look, but said that it could be a number of different problems (pump/boiler/hot water tank/radiators), and so I've been trying to narrow the options down a little, rather than agree to replace parts that might in fact be ok.

So here is what I think I've found out:

1. It seems to be related to heating only, as the problem first starts about an hour after the heating has been on in the morning (we only heat the water for an hour each evening).

2. Before the tank overflows, the boiler sounds like it is 'over-boiling' (kettling?), then the pump makes a noise (like it is cavitating). The water then seems to be travelling up the pipe into the F+E tank before overflowing. Then the pump and the valves make lots of noise before the whole system goes quiet again. The pump and the pipes get too hot to touch during this process.

3. I don't believe it is a problem with the cold 'feed' into the F+E tank as it is a random overflow (not a constant flow), and I've recently replaced the ball valve in the F+E tank and adjusted the water level accordingly.

4. Also, the boiler seems at random periods throughout the day to be trying to switch on, but then immediately stops firing up. I guess the system might be demanding heat, but the overheat thermostat might be stopping it from firing? (I'm afraid I haven't checked if heat is actually being demanded when it does this).

5. Prior to this problem, the boiler thermostat was set at about 3.5 (on the dial of 1-6), and I've since turned it down to 2, but the problem remains.

6. During the whole period of this problem, the radiators get ever so hot, despite all (but one) having TRV's which are generally set at about 2 out of 6 on their dials.

7. One radiator has never worked in all the 3 years we've been in the house. Physically it is in the room above the boiler, but I don't know where it sits in the plumbing loop (as it were).

8. All radiators have been bled, and I've never got any any air out of any of them.

So taking this all into account, I'm now at the point where I think it is a problem with the boiler thermostat. I've purchased a replacement overheat thermostat, but I'm now thinking this part probably is still working, as the boiler does stop firing sometimes when (I believe heat is being demanded).

Would I be right to now conclude that the thermostat (thermistor wire?) is possibly at fault, and that the problem is arising because the boiler cannot regulate the water temperature correctly, making the boiler 'kettle' and overflow into the F+E tank?

I'm confident that the hot water cylinder coil hasn't split because the problem happens when the hot water is not being heated.

Admittedly I guess it could be a Zone Valve Actuator fault - which could be diverting hot water into the hot water cylinder undemanded? And furthermore, I haven't dome much to investigate if the pump or ZVA'a are themselves working correctly (although the heating engineer who came did say he thought the pump was working ok).

Finally, this whole problem did seem to start about the time I changed the old thermo-mechanical room thermostat for the Horstmann digital one, and whilst I'm confident I wired it up correctly, it's entirely possible I've made a fundamental mistake with the wiring (from 4 wires to just 2 in the DRT2) - so could this be the problem. (I've still got the old thermostat, so could put that back in place to troubleshoot - but haven't done so yet).

If you can offer any advice I would be most grateful.

Many thanks,

Matt.

 

[petit_pablo]

More likely to be a partial restriction between the open vent & cold feed the system pumps over more when the heating is on as you are heating a much larger volume of water and the expansion of this exagerates the issue.

Without knowing what the actual temperatures of the flow & returns to the boiler are its impossible to say if that boiler stat is out of calibration.

The overheat stat on the classic requires manually resetting so doubt its overheating

 

[Agile]

Its almost certainly caused by sludge.

Allowing a system to pump over will cause serious further sludge buildup.

8mm microbore can be very difficult to clean.

Microbore is far better on a sealed system.

Tony

 

[EmJayDee]

petit_pablo,

How would I go about diagnosing that as a fault? How can I check the pipes for blockages - or is it just a case of flushing the systems out?

Matt.

 

[EmJayDee]

Tony,

So a sludge build up is causing the problem? Does that mean the pipes/system are blocked, resulting in restricted flow, hence the hot water that cannot be circulated returns to the F+E tank rather than flowing round the system?

The heating engineer who came did say that a flush might help, but that it also might not work (presumably because of the difficulty with the microbore).

I should have said in my first message, I did turn the Pump speed down (from 3 to 2), and whilst the problem still exists, the associated noises seem quieter. That could coincide with a blockage because the pump is now not trying to shift as much water, hence I'm not getting the problem as badly as before?

As you can tell, to a novice, this is all a bit confusing, as there are so many potential causes.

Thanks for your help so far.

Matt.

 

[petit_pablo]

I should have said in my first message, I did turn the Pump speed down (from 3 to 2), and whilst the problem still exists, the associated noises seem quieter. That could coincide with a blockage because the pump is now not trying to shift as much water, hence I'm not getting the problem as badly as before?

Matt.

Yes, this will reduced the pump pressure on the circulating water.

If everything is getting hot then you could try adding system cleanser to the system and letting that circulate for a week then draining out and refilling until water runs clear then dose with inhibitor. This does run the risk of bunging up the heating manifolds though.

 

[Agile]

I generally find that the only usually effective way of cleaning microbore is a citric acid based chemical like DS40 in the round tub.

But that runs the risk of leaking rads and valves.

Tony

 

[EmJayDee]

petit_pablo,

Thanks again for the advice.

Draining down the system sounds a bit out of my league - so getting a pro in would save me getting in trouble with the Mrs when I flood the lounge with black sludge.

Where is the heating manifold - in the boiler itself?

Matt.

 

[EmJayDee]

Tony,

So this acid based chemical flusher would basically eat away at the copper/steel in the system as well as the sludge, which could give me more problems?

If I can never properly 'clean' the system, will I continue to get problems, and will I have to look at getting the whole heating replaced sooner or later? Or is it a case of keeping the system filled with some sort of inhibitor to keep problems to a minimum?

Matt.

 

[nogoodatfaultfinding]

petit_pablo,

How would I go about diagnosing that as a fault? How can I check the pipes for blockages - or is it just a case of flushing the systems out?

Matt.

Get a STRONG magnet and place it on the pipes (RUN IT ROUND THEM ALL) in your cylinder cupboard.
If it sticks ANYWHERE its a blockage and you should look at a cylinder cupboard repipe and flush!!!

 

[EmJayDee]

nogoodatfaultfinding,

Thanks for the advice - that is something the heating engineer did suggest, but we didn't have a magnet when he came.

So you're suggesting that if I find a blockage, it's unlikely to be shifted with a flush (power or chemical), and instead I should get the pipes replaced? That sounds quite 'severe', but makes sense as people have commented that sludge/blockages seem hard to shift in microbore.

Matt.

 

[EmJayDee]

All,

Obviously I'm a heating numpty with no training/expert knowledge, but I'm struggling to understand why the radiators are getting so hot (and the pump/pipes etc) if it's all caused by sludge.

Is it just because the 'system' isn't allowing the proper flow of water due to restrictions caused by sludge/blockage, hence heat isn't dissipating like it usually would?

I'm still strangely drawn to the problem being caused by a faulty boiler thermostat - but no-one has suggested that as a potential cause yet (except me!).

Matt.

 

[petit_pablo]

How hot the system is perceived to be is down to your judgement. I know once a pipe gets much past 55degC i canth hold my hand on it for long. 65deg and above forget it.
Without measuring the actual temp its hard to say whether the boiler stat is faulty or not.

 

[EmJayDee]

petit_pablo,

Fair point - I guess the pipes could very easily be cooler than they appear to me.

Time to get a thermometer then.

Matt.